By Carl Strohmeyer
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Keeping a clear garden pond in the warm or hot summer months involves these key ingredients:
Proper filtration (especially biological) and circulation, cleaning and maintenance, proper chemistry and feeding. It is also noteworthy that well built pond that is in harmony with nature needs much less maintenance.
This article will also deal with winter care tips, pond predators such as Herons and much more.
Placement of your yard pond is important, despite popular belief a pond is best placed above any low spots in your property as drainage from a rainstorm (or even over watering) can foul your pond adding many unwanted nutrients and more. The sides of your pond should be built up at least a few inches. I also recommend a minimum depth of 24”. Obviously a raised patio pond will not have this issue.
Done right, a well set up and maintained pond improves the beauty of your home and garden and this regularly updated article, as well as the useful links to other resources such as Veggie Filters, UV Sterilization, and Pond Algae (green water) should help the reader achieve this with a garden or patio pond.
Please note that while I recommend specific pumps, filter, UVs, and other pond equipment; for the most part these recommendations are based on years of use (for reliability, efficiency, and economy) by me and/or other pond keepers and professionals I trust for their input; NOT what some pond supply distributor has suggested!
My experience and the other pond keepers I get input from is generally for ponds up to 8000 gallons, so admittedly for much larger ponds, any prospective reader might find some great information here, but need to go further for added information.
Also PLEASE read the many additional resources already supplied here.
 ADEQUATE WATER CIRCULATION AND MOVEMENT (Pumps).
A general principle (not a rule) of about 50-200 gph per 100 gallons can work for this (A lower proportional gph for large ponds, a higher proportional gph for small ponds). This can be achieved with more than one water pump.
A large aeration device (air stone) coupled to an Air Pump can also aid in circulation and are especially useful for “lifting” (vertical circulation) water from the bottom of a pond when properly placed. Often an air stone/air pump combination is better than water pumps of greater gph for the aspect of vertical circulation (keep in mind that an air stone aerates the water by breaking surface tension, not by the bubbles in the water; the more surface agitation, the better oxygen exchange).
A large double air pump such as a Fusion 700, Million Air 600, Whisper 800, or Maxima with two air stones can circulate at a rate up to 500 gph. A way to check this is to place the air stone down a narrow PVC tube or aquarium lift tube, then place the top of the tube just above the water level and measure the rate the water fills up a gallon container (one gallon in 15 seconds= 240 gph).
*Fusion 700 Air Pump
*Million Air 600 Pump
With any pump (Water or Air), at least some form of circulation should be provided 24/7 so as to provide both oxygen and also to maintain a healthy bio filter (this also means a pump connected to a filter should run 24/7). Most pumps properly placed do not disturb fish, based on my experience.
General Pond Pump Recommendations:
For cross circulation (& lifting water to water features), a water pump is the primary choice.
To start with the Rio HF Pump line is an excellent line of pumps for most ponds from 300 to even 6000 gallons from my experience as these pumps have top notch head pressure, they are reliable and have flow rates up to almost 2000 gph.
What I have found is that even with larger ponds having multiple reliable and powerful pumps such as the Rio 32HF, I have more redundancy, more flexibility, and simply less "disasters" with a single "super large" pump pond.
As an example, I set up a 3000 gallon pond with three 2000 gph pumps feeding a fountain, veggie filter, two UV Sterilizers, and a DIY barrel filter and then a waterfall with good aesthetic flow.
Product Resource: Rio HF; High Flow Rate & Head Pressure Pond Water Pumps
To protect your pump from large debris (that can damage the impeller and impeller housing), placing any water pump off the bottom of the pond on a cinder block or similar can keep large debris from quickly clogging pump intakes.
Please click on the pictures to enlarge for a better view
For further protection, you can place your pump in a DIY bucket (or box, etc.) pre-filter, or simply cover the pump with 1/2" to 1" rocks (porous lava rock is best).
Besides protection from debris, this added pre-filtration will provide added biological filtration.
This is especially useful for pumps added solely to run UV Sterilizers due to added pre-filtration.
METHOD: Use a bucket, box, or similar container large enough to house the pump; then add Volcanic Rock about ½” in diameter or larger, an outlet tube, then either seal the container with holes in the top OR simply leave the bucket, box, or similar container open with only the rocks/gravel exposed.
To the left is a diagram of how this would basically work.
I recommend some sort of rock pre-filtration or similar with ANY submersible pump!! From my experience this GREATLY extends pump life regardless of any manufacturer claims as I have had very expensive pumps with so-called built in pre-filters fail in one season without this rock pre-filter.
Product Resource: Volcanic Rock Bio/Mechanical Filter Media
For small to medium ponds (100–800 gallons): the SunSun HQB Series Pumps, or Rio 1700 all are proven in professional pond maintenance to be efficient and reliable, as well as reasonably economical pumps (the Rio 1700 has an available water Fountain Kit).
Both have sealed electromagnetic motors and ceramic shafts.
*Medium Duty Pond, Fountain Water Pump; SunSun HQB Series
*Taam Rio 1700 Water Pump
The lighter duty SunSun JP-066 can also be used in ponds, however I recommend using either the Filter version or making a pre-filter bucket to protect it due to the standard JP-066 pump not having a pre-filter (described below, which is a good idea for any pump unless a Hydro Pond Pre-Filter is used, which cannot be attached to a JP-066).
Many pumps, such as the Rio and SunSun can be mated to a Fountain Head with built in diverter then connected to a Filter (such as a small Pressurized Filter), and a UV Sterilizer (such as the TMC 15 Watt Pond Advantage PRO UV) for up to a 500 gallon pond
*SunSun JP-066 Pump
*Pressurized Pond Filters
For medium to large ponds (500 – 1500 gallons);
For even more head pressure for high pond features (such as a water fall or spitter) that require lifts of much more than 6 feet the Rio HF Water Pump line is without comparison with their Vortex Rotor Blade (which can lift up to 14 feet), especially for the price.
The SunSun JAP-8500 Amphibious Pond Pump can also be used for medium to large ponds (generally over 1000 gallons), especially when its multi-purpose versatility is needed such as running a larger fountain, powering a pressurized pond filter, and circulating water to a Veggie Filter all with one powerful pump
*Rio HF Water Pump line
*SunSun JAP-8500 Amphibious Pond Pump
For Very large ponds; often the best way to go is with a heavy duty submersible pump with a directional vortex impeller or a pool/spa style pump that is designed for the harsh pond environment (some pumps cannot stand up to the debris and other elements of pond water circulation).
This said, my preference even with the 6000-8000 gallon ponds I have plumbed, I vastly preferred the redundancy of two or more heavy duty submersible or 'amphibious' pump such as those suggested in the next paragraph over these pool/spa pumps such as the Seahorse.
This way if one stops/fails for whatever reason, your pond will still be circulating; nothing is more frustrating than coming back from a summer vacation to find a stagnant & smelly pond with a dead pump
As well two or more somewhat smaller pumps will almost always provide a better flow pattern and work better with most filters and UV Clarifiers.
The SunSun JAP-8500 Amphibious Pump at 2245 gph or the ultra efficient SunSun JTP-12000 High Efficiency Pump that produces 3170 GPH FOR ONLY 100 Watts are excellent heavy duty submersible pumps.
For "out of the water" pumps, the Pentair SeaHorse line of pond pumps offers flow rates up to 4900 gph and are very well made reliable pumps that usually handle the harshest of conditions.
For those needing an out of the water pump of lower cost & more versatility, the 'Amphibious' (in line OR submersible) SunSun JAP-8500 might be a good choice.
*SunSun JTP-12000 High Efficiency Water Pump
*SunSun JAP-8500 Amphibious Water Pump
For these heavy duty 1/2 to 3/4 hp pumps, Heavy Duty submersible Pumps, or similar I have generally used 1.25 to 1.5 inch PVC pipe and then split the return pipe suing PVC ‘Ts’ and valves to control flow through other pond filters such as a Pressurized Filter and a UV Sterilizer. The purpose for this is to run multiple filters, UVs and/or to have a slower flow through these devices which generally work much better than at the high flow rate provide by this type of pump.
Using PVC 'T' Diverters also allows for the use of these large pumps for smaller ponds under 1000 gallons where multiple features and/or high head pressure features are being run.
Even with a large pump like the SeaHorse, I still recommend another smaller one for redundancy in case of failure, and often for large ponds I simply use several pumps like the Rio 32H
Product Resource: Rio 32H 1590 gph Heavy Duty Pond Water Pump
is VERY important in ponds (partly for the Redox Balance). All oxygen is exchanged at the surface, so good surface agitation over the entire pond is best. Waterfalls, fountains, air stones all can achieve this.
Low dissolved oxygen levels and a low KH & GH (below 50/100 ppm respectively) affect your fish’ ability to perform osmoregulation & Redox Balance will be poor. If these parameters are poor, this will allow for much more opportunistic infections.
Further Reference: Aquarium Answers; Fish Osmoregulation
The fountain head in the picture to the left (click to enlarge) is an excellent way to aerate.
Some examples/product resource are available here:
*Rio 1700 and Fountain Head
*SunSun Fountain Head.
Make sure in winter months to de-ice and circulate water to the surface for optimum fish health.
For further information about GH/KH, please see this article:
CALCIUM, KH, GH, IN AQUARIUMS & PONDS
For further information about Redox Potential, please see this article:
REDOX POTENTIAL IN AQUARIUMS & PONDS; How it Relates to Proper Aquatic Health
 GOOD FILTRATION.
Good filtration, especially biological is essential to maintain a healthy pond with the only exception being with a “flow through/spring fed” pond.
Understanding the Nitrogen Cycle, which is the same in a pond as in an aquarium with the added input of debris from trees, wind borne, and sometimes wild/domestic animals adding to this strain on the bio system.
More than one filter is always best when possible and this includes DIY natural plant/veggie/bog filters which add to the aesthetics and are an enjoyable DIY project in my opinion.
Aquarium and Pond Nitrogen Cycle
Multiple types of filtration in combination are also excellent, such as these to name a few: a pressurized filter, bio falls combination, sponge filter, fluidized, barrel, and/or veggie filter.
While popular, I personally do not care for pond skimmers as these often tend to trap water lilies, hyacinth, and other floating pond plants all the while providing little to the quality of pond filtration (other than removal of floating leaf debris, especially in autumn).
I have found when I took over a pond care contract for a client that already have a skimmer, I would later disconnect the skimmer after adding a Veggie Filter. In the end, the pond actually was MORE clear with more natural looking floating plants too!
The picture to the above/left shows a Via Aqua Multi-Purpose Pond Pump embedded in loose volcanic rock (for added pre-filtration as noted earlier) connected to a Pressurized Pond Filter and then to a High Output Pond UV Sterilizer/Clarifier.
This picture displays how a large pump (as shown with the high flow VA Pump) can be utilized for more than one function, including multistage filtration, UV Sterilization, a fountain and even can be diverted for watering a Veggie Filter.
Please note that a control valve may be needed on both sides of the diversion ‘T’, otherwise the water will follow the “path of least resistance”, put another way if your water flow is too slow through the UV Sterilizer/Filter side of this example, it may be that the return is too high above the other return and simply lowering the return will solve this problem. As well after splitting a return line, the lines should not be combined later in the return. Please read the UV Sterilizations section for more on this subject.
*SunSun Premium Pressurized Pond Filter with UV
*TMC Pond Advantage Premium VERY High Output UVC Sterilizer
I do not recommend the Pond Master Submersible & especially the Becket filters as they come out of the box; they clog easily and are not efficient filters unless modified.
However the Pondmaster 1000/1700 can be vastly improved by unscrewing the screws in each corner and adding volcanic rock biological filter media to this area under the tray (as the Pondmaster only utilizes two pads that only perform mechanical, some chemical, & NO essential bio filtration).
In fact the PondMaster can be a reasonably good filter for the money if purchased with this volcanic rock, however most sellers of this filter sell it on the "cheap" and unfortunately do not include this.
Pondmaster Submersible Pond Filters UNIQUELY sold ONLY at AAP with Volcanic Filter Media
Volcanic Rock is excellent for this or BETTER yet would be SeaChem Matrix. Both of these would add considerably to bio filtration of your pond by adding to your filter.
*Volcanic Rock; Nitrifying and de-nitrifying Filter Media
*SeaChem Pond Matrix; High porosity media
In fact Pond Matrix provides the best internal macroporous surface area of ANY product and is an excellent compliment to a pressurized filter, waterfall filter, drum, or large sand/bead filters such as the AquaBead.
These macropores are ideally sized for the support of nitrifying and de-nitrifying bacteria. This allows Pond Matrix, unlike other forms of biomedia, to remove nitrate along with ammonia and nitrite, simultaneously and in the same filter and rarely if ever needs to be changed if properly cared for.
Pond Matrix also makes an excellent support for root development of aquatic plants and may be used for Pond Veggie/Bog Filters or in pots
I also suggest replacing the black carbon impregnated pad in the Pondmaster with a cut to fit Poly Pad and add carbon or Zeolite underneath the tray (also in a filter bag).
*Poly Pad Micron filter media
*API Ammo Chips Zeolite Filter Media
I prefer pressurized pond filters such as the SunSun UVC Pressurized or others for their efficiency and ease of hiding in the ground.
These filters include the popular Tetra, Lifeguard Pressurized, and Cyprio, which are excellent too, but tend to be over priced, especially considering Tetra charges almost $200 more for their UV feature when a separate and VASTLY better TMC Pond Advantage would be better (see the UV Section of this article).
Product Resource: Pressurized Pond Filter, SunSun Model CPF-250
The SunSun model pictured to the left, is not much different in design than other pressurized filters, rather what sets it apart is that it is also is supplied with highly bio efficient volcanic rock and and yet is still a lower price and is my recommendation!
Pressurized filters can be buried in the ground or place behind a water feature easily. Pressurized pond filters are very good bio filters especially when price is considered and these are also excellent mechanical filters.
However many if not most pressurized pond filters are sold with attached/built in UV Sterilizers which when the flow rate/dwell time is considered usually provides only some green water clarification and absolutely NO level one sterilization.
A SEPARATE UV such as the TMC Pond Pro Advantage is vastly more effective when plumbed properly including placed after an otherwise excellent pressurized pond filter.
Product Resource: TMC Pond Pro Advantage TRUE Level ONE UV Sterilizers
Further Reference, a MUST Read for pond keepers!!
UV Sterilization; Facts & Information; How Ultraviolet Sterilizers work in ponds
Do NOT confuse an aquarium canister filter with a pressurized pond filter, where as although a pressurized pond filter can be used for an aquarium, the use of an aquarium canister filter for a pond will result in failure since most aquarium canister filters have top mounted motors that will loose their siphon in most pond applications, as well an aquarium canister filter is not nearly as rugged in design for the pond environment (I had a couple of service calls many years back where customers attempted to utilize an aquarium canister filter for their pond and results were not good!).
Small or Patio Pond (under 250-500 gallons depending upon fish stocking and natural debris fallout);
For small ponds and patio ponds (ponds built in above ground "Rubber Made" or other similar containers such as converted horse waterers), large sponge filters are excellent bio filters and reasonable mechanical filters. They are inexpensive, easy to service, and simple to attach with either a power head pump or and air stone.
There now is a specific patented Pond Sponge Filter called the Hydro-Pond by ATI, with three models; one air driven, two pump driven. They are useful up to 1500 gallons and more can be used for larger ponds or in combination with other filters. The Hydro Pond IV also makes an excellent pre filter for pond pumps before water is circulated to another filter such as a pressurized filter.
For "patio ponds", these filters can perform very well since the only weakness is inability to handle large debris, but with patio ponds this is rarely a problem. In fact one client of mine with a 150 gallon patio pond had a small Becket pond filter he purchased at Home Depot that did not keep his pond clean, however when he switched to a Hydro Pond #2 his water while still somewhat green was much more clean and the fish could be readily seen.
I highly recommend the Hydro Pond filters for small pond owners on a budget, owners of patio ponds, or just to add redundancy to existing pond filters (often is larger ponds)
Product Resource: Patented Hydro-Pond; Sponge Filtration for Pond
A top notch (& unique) filter for ponds up to 500 gallons would be a TMC V2 1500 Fluidized Filter when combined to a pre-filter system as pictured to the left.
This system would work for larger ponds when multiplied such as two for up to a 1000 gallon pond.
The "SunSun CHJ-1503; Small Pond Pump/Filter", "Pondmaster 1700" (small to medium pond) are other reasonable filter choices for small/medium ponds under 500 to 1000 gallons. These filters along with the Hydro-Pond Sponge and Fluidized are an excellent compliment to a Veggie Filter (which I recommend for any pond).
With the SunSun CHJ-1503 or similar Submersible Pond Filter you can easily attach a UV Sterilizer to the “diverter” valve (just above the filter and below the fountain head) for improved water clarity. A UV Sterilizer can also be added to the diverter valve of a Pondmaster 1000-1700 filter or similar as well.
See the UV Sterilizer section further in this article for a diagram.
*SunSun CHJ-1503 Pond Filter With Fountain
*Pondmaster 1700 WITH Volcanic Rock only at AAP
*Premium Fluidized Sand Bed Pond or Aquarium Filters
Medium Pond (250-2000 gallons depending upon fish stocking and natural debris fallout);
Bio falls such as the Savio Livingponds Filters are also excellent pond filters for medium and many larger ponds.
These filters can also be DIY (Do it yourself) or you can start with a basic Bio Falls “skeleton” filter (pictured to the left) and then add bio filter media (such as Volcanic rock) and place a Polyester Media on top.
However if you have purchased a unit such as Savio Livingponds Waterfall filter, you can add extra media to meet your pond needs and possibly save money. For instance I have often substituted Volcanic Rock of different sizes (depending on coarseness of filtration needed) for bio and mechanical media in these and similar filter.
This article about Aquarium filter media can also be applied to ponds:
Aquarium & Pond Filter Media, Material; Mechanical, Bio, Chemical
Plastic grates and even rocks formed into basin can be used to construct the bio and mechanical filter for flow through either prior to a water all or after (prior is more common). If a cement product is used in construction, I recommend sealing it with a water proof sealer available at most Home Improvement Stores.
Use of volcanic rock for bio filtration and Coarse Polyester Media (pictured to the left) can help with the filtration need of your bio falls project as well as other similar projects such as a Veggie Filter pre-filter trap.
Product Resource: Coarse Poly Pads; Excellent for DIY Pond projects
*As noted earlier, Pressurized Pond Filters are an excellent choice for medium ponds. These can used with other filters for improved filtration and redundancy or even larger yet ponds.
You can also use multiples of Pressurized Pond Filters for larger ponds. As well even a smaller pond can utilize these simple yet effective filters, especially where the bio load is high.
This is probably one of my favorite pond filter types to use either by itself, in multiples or often with other pond filter types.
Two aspects of this filter type I like is their ability to go inline from the pump to any water feature, such as a water fall, while maintaining water pressure (no need for gravity feed). The other aspect I like is these can be partly buried to improve the pond aesthetics.
Product Resource: SunSun Premium Pressurized Pond Filter
*Another filter that works well with small and many medium sized ponds is the barrel style filter by Tetra and Coralife; these are excellent bio filters, but poor mechanical filters. They also are hard to hide as they have to use gravity to return water back into the pond after the pump first supplies these filters with un-filtered water.
This filter too can be a DIY project using a large sterilized drum.
Pond Filters of Note & Larger Pond Filters:
*A filter that is also used is pool style sand filters. I have used these filters in many of my largest pond installations (over 5,000 gallons).
Despite what pundits for these over priced monstrosities say, they are not originally designed for ponds. The fine sand therein will often compact and the water then tends to follow the path of least resistance thru these filters, leaving areas on anaerobic bacteria producing poisonous Hydrogen Sulfide.
DO NOT be fooled by their high price (often well over $1000), I can tell you from vast experience with them that they are not worth it!!
That said, if you already have one, I recommend adding volcanic rock and/or SeaChem Pond Matrix to improve upon this problem and also allow for nitrate removal via de-nitrification.
*Fluidized Sand or Moving Bed Filters;
These types of filters are purely for nitrifying (removal of ammonia & nitrites but not nitrates), however they are excellent at performing this task (and in fact the BEST)!
I do recommend pre-filtration of some sort such as coarse rocks near an intake or at the very least a coarse mesh screen to allow for maximum effectiveness.
Of these types, the Fluidized is the most efficient from what I have found, especially the third generation models such as the TMC V2 1500 Fluidized Filter. However these standard Fluidized Filters are only capable for ponds up to 500 gallons unless multiples are used or as a compliment to other filters.
Product Resource: Premium Fluidized Sand Bed Pond, Aquarium Filters
The Nexus Moving Bed Filter or TMC Pro Pond Fluidized Filters should be considered for large ponds as their design lends itself better especially to ponds over 2500 gallons.
In fact at approximately $800 retail, you will not find a better aerobic bio filter than the TMC Pro Pond FBF80 Fluidized Filters with the capacity to handle 176 lbs of bio mass respectively (this is a LOT of fish!). This works out on average to a 2500 gallon to 5000 gallon pond. Their size alone belies their large pond capacity with the FBF80 measuring 61 inches tall and 13 inches wide.
Future Product Resource: TMC Pro Pond FBF80 Fluidized Filters
For a serious pond keeper this would be the filter of choice by a wide margin, even over the Nexus Moving Bed Filter (which is still a top notch pond bio filter)!
With either of these filters, I would strongly recommend a DIY Veggie/Bog filter to provide nitrate removal via plant roots end de-nitrification.
DIY Pond Veggie, Bog Plant Filters
To the left is a diagram of a basic "DIY Gravity Flow In-Line Pond Filter" (principle is similar to Tetra or Coralife barrel filters).
Click picture to enlarge
Volcanic rock makes an excellent filter media for DIY pond filters, waterfall filters, veggie filters (for the base), and many types of commercial filters such as the Savio.
Please click on the picture for more information.
For information about different filter media that can be used in your pond filter, please visit this article:
Aquarium and Pond Filter Media
 PLANT FILTRATION (Often called Veggie Filters);
This is a very important part of pond keeping and filtration.
A well planted and diversified planted pond is VERY important for clarity (including green water control), pond and fish health, and even fish breeding.
Any plant with a good root structure that grows fast and has the majority of their leaves above water is a good candidate to start with. I recommend water iris for their strong root structure, fast growth, great nutrient absorption, and a great place for baby fish (fry) to hide feed and grow (if you use an “in pond” Veggie Filter).
There are many other excellent plants as well such as Cattails, Sweet Flag, Parrots feather, Bluebells, Umbrella palm, Papyrus, & bull rush. Make sure these types of plants (plants with roots in water and leaves above) are planted in an area of good, but not strong water movement. This ensures that they will do their job as plant filters.
Other plants such as lilies and hyacinth are reasonable for nutrient removal too, but not at the rate of iris and similar plants. These plants also do not have the root structure that will aid in the rapid removal of nitrates and ammonia, and thus should not be a part of a true Veggie/Plant filter.
However, these floating plants are useful for shade, which will slow algae growth.
I will off place this plant filter in an area of water constriction between two ponds or in an upper waterfall area with low to moderate current. In smaller Ponds I will just place this plant filter in a corner of the pond with a small water current applied to the planted area.
I prefer my plant filters within the pond as these look more attractive in my opinion and give the fish fry a place to hide (except in the case of the waterfall or cascade plant filter).
The area of the Veggie Filter should be relatively shallow as well to force water movement over and through the roots. I also recommend ½” -2” rock under the plants to allow the roots to better establish themselves, do not use sand or soil.
Other methods include separate veggie filters in containers or pools. I am not as fond of this method for the reasons above, however these do work.
Click picture above to enlarge
FOR MY FULL VEGGIE FILTER ARTICLE, please visit this link:
POND VEGGIE (BOG PLANT FILTERS)
This article includes much more information on this subject, as well as links to resources for bog plants and similar.
The bottom line is few ponds in my opinion are truly complete without a "Veggie/Bog Plant Filter" as they can make a big difference when done right in pond clarity.
As an example, I had one pond I built for a client that had such a large and efficient Veggie Filter that it stayed clear without the UV Sterilizer running.
For those who read this, please note that in my emphasis of the use of Veggie filters is not driven by financial gain, that although I obviously list products to sell through my many articles (as a means to pay for the time to keep these articles up to date), I have little to gain since Veggie Filters are primarily a DIY products.
 UV STERILIZATION (& Algae Control):
Although not always necessary in a well planted, well shaded, well filtered aquarium; these devices are still very useful. UVs help with algae control, disease prevention, and the Redox potential (which is important for fish health and proper filtration).
The time it takes to clear a green pond with a UV Sterilizer/Clarifier can vary greatly from 1 day to a couple weeks to even never!
The reason for such wide variance is due to lack of adequate filtration, especially a good bio filter such as a veggie filter or use of denitrifying products such as SeaChem Matrix or Volcanic Rock, and simply an inadequate UV Sterilizer and/or one that is properly plumbed. It is also noteworthy than many so called UV Sterilizers are in fact ONLY capable of UV Clarification and therefore should be labeled as UV Clarifiers, but are unfortunately improperly labeled as Sterilizers.
For the UV to properly function in a pond for green water control (UV Clarification), the flow rate should not exceed 40-50 gph per watt of UVC in most Compact UV Sterilizers (such as the Tetra, or Terminator), or 50-70 gph per watt for most higher dwell time straight tube UV Clarifiers (some super high efficiency/dwell time UV Clarifiers such as the TMC Pro Clear UV30 can go to over 70 gph per watt). Keep in mind these numbers are for UVC Clarification, not level 1 sterilization (which requires slower rates and higher pond or aquarium turnover).
Product Resource: TMC Pro Clear UV30
In larger ponds with high flow rates I often recommend more than one UV sterilizer, with a by-pass from the main line to control flow rate, then each unit connected in parallel for best results, although in-line can work too, just not as effectively. Often a separate, slower pump (with a pre-filter) installed for the sole purpose to run the Pond UV sterilizer is the key to success when the main pump line runs at too high a flow rate for the UV to be optimally effective.
For this reason, I also do NOT recommend the popular filters with built in UVs as your Pond's sole UV Sterilizer/Clarifier.
The flow rate is usually too high to work properly. As well, the design of most I have seen and used have too high a gap between UV bulb/quartz sleeve sterilizer compartment wall, which is generally not adequate for good UVC exposure. The FACTS are that these filters with built in UV lights are UV Clarifiers AT BEST, and even then poor UV clarifiers
A separate UV is always best! I have maintained ponds with UVs in filters and UVs separate and the difference in water quality in the separate UV ponds is significant!
What is also noteworthy is that while a basic UV Clarifier can clear green water when properly installed, it WILL often takes days when under the SAME conditions a TRUE level one or higher UV Sterilizer (especially a high dwell time model) can take just a day or two or even as little as just hours while also having the bonus of improving fish disease resistance (via improved Redox Balance).
For more information about correct Pond UV sterilization and how it works please visit this site;
"HOW TO USE A UV POND OR AQUARIUM STERILIZER"
Many times I have heard of complaints that their UV did not help with algae control, when I checked this clients pond, I found inadequate filtration and an improperly installed UV sterilizer. Even a properly installed True UV Sterilizer cannot over come poor filtration and a poorly planted pond. As well, many manufacturers make claims of high flow rates that are impossible for proper contact time.
Another common problem I have encountered is a poor circulation pattern where-by the water pick up for the UV Sterilizer was near the water return, with the result that 3/4 or more of the pond water never made it into this flow pattern for proper UVC Sterilization.
POND UV WITH BYPASS APPLICATION DIAGRAM; Click picture to enlarge.
To maintain a proper flow rate per watt per gph, connect a ‘T’ in line to your high flow rate pump, from there a reducing bushing (Ex. In 1-1/2” PVC I would step it down with a 1-1/2” by ¾ bushing), from there an in-line ball valve, from there to your Pond UV Sterilizer, then back to your pond or water feature (such as a waterfall or spitter).
Another option is to split the outflow from a large, high output pump and place a UV Sterilizer on each line.
As an example with a 3600 gph pump (of which these gph flow ratings are based 0 head pressure and after real world applications that include lifting of water the actual flow would be less) could be split and two TMC Pond Advantage UV Sterilizers (or equivalent) placed on each line
You can also simply add a separate lower rate pump just for your Pond UV Sterilizer.
The picture to the left depicts a UV flow diverter for use with high flow pond (or aquarium) pumps so as to achieve correct gph/per watt flow rate through the UV Sterilizer.
These diverter valves are listed/sold here: Pond/ Aquarium Plumbing Parts
Please note that these diverters only represent a fraction of PVC sizes and combinations, as well a ball valve may also be necessary on two sides of the diverter if head pressure is too high on the UV Sterilizer return side.
Here are a few solutions if the flow is too slow through your UV Sterilizer:
- Add a ball valve to the other outlet to force more water through the UV Sterilizer
- Lower the return for the UV Sterilizer to a place in the pond that is lower than the primary return, thus lowering head pressure through the UV and thus increasing flow.
- Do not recombine the two (or more) return lines down line before entering the pond, this interrupts water flow and will increase back pressure and reduce flow. All return lines must enter the pond separately!
This diagram shows a Via Aqua BH2000 Filter/Pump (similar to the before mentioned Pondmaster or SunSun Pond Filters) connected to a UV Sterilizer via the built in diverter valve. This valve is common to most similar fountains and filters such as the Pondmaster 1700, SunSun CHJ-1503, and many more.
Please click on the picture to enlarge for a better view