POND CARE INFORMATION; From Filters to Maintenance for a "A Clear Pond"
By Carl Strohmeyer-PAMR 35+ years experience
Keeping a clear garden pond in the warm or hot summer months involves these key ingredients:
We have to remember too that a pond is living organism, unlike a swimming pool. Essentially a pond is an aquarium with the added bio load of leaves, pollen, run-off and other debris often being added to our aquatic environment.
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.
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!
In the case of UV Sterilizers, I have VERY extensive experience, from designing, application, experimenting with controlled tests and more; so my recommendations for true UV Sterilizers (including specific brands there in) is based on this considerable experience and the use of equipment other than recommended will likely NOT yield the same results, especially based on email from those who have read this article but still chose a different path for this important equipment!!
Finally, my experience and the other professional 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 such as those cited for Veggie Filters or UV Sterilization.
 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).
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:
In my many years of pond maintenance using many different brands, I have found that regardless of what a pump manufacturer or retailer tells you, ALL POND PUMPS ARE EASILY CLOGGED OR EVEN QUICKLY RUINED BY DEBRIS!
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).
METHOD: Use a bucket, box, or similar container such as a Rubber Maid 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. A void space next to the pump intake will also extend time between rock rinsings.
Product Resource: Volcanic Rock Bio/Mechanical Filter Media
It is noteworthy that this rock will likely need to be cleaned ever few weeks to a month depending upon bio load and whether or a not a REAL filter is also employed.
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).
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).
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
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' pumps such as those suggested in the next paragraph over these pool/spa pumps such as the Seahorse.
The AAP/SunSun JAP-8500 Amphibious Pump at 2245 gph, the JAP-18000 at 4755 gph, or the ultra efficient AAP/SunSun JTP-12000 High Efficiency Pump that produces 3170 GPH FOR ONLY 100 Watts are excellent heavy duty submersible pumps (pictured above).
In fact, as these AAP/SunSun JTP-12000 pumps have now been out for a while, these have really impressed me as "the pump to have" for any high flow submersible application due to reliability, flow and super high electrical efficiency!! While the purpose of this article is to provide helpful information not to "hard sell" items, I feel I really need to point out that is you are need of a pump in this flow range, this one is one that certainly should be considered.
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 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.
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
Sometimes flexible/vinyl tubing will be difficult to connect, however by lubricating the connection, then heating the tubing, along with clamping with a standard hose clamp in some instances, this should not be a problem. This works for clear, black and ribbed tubing.
For further Water Pump Specifications & Tips, please see:
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:
For further information about Redox Potential, please see this article:
 GOOD FILTRATION.
As per the overview section of this article, most often ponds I have consulted for over the years are woefully under filtered for the given bio load.
Multiple types of filtration in combination are also excellent, such as these to name a few:
Readers might note that I did not include skimmers in my list above. 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).
The picture to the above 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.
I generally 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.
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.
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.
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).
I prefer pressurized pond filters such as the SunSun UVC Pressurized or others for their efficiency and ease of hiding in the ground.
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.
Further Reference, a MUST Read for pond keepers!!
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!).
SUGGESTIONS (based on pond size), please note a DIY Veggie Bog filter qualifies in ANY of these pond sizes:
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.
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.
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.
The "SunSun CHJ-1503; Small Pond Pump/Filter", "Pondmaster 1700" are other rgood 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.
Another way to add filtration as well as a UV Clarifier is to use one of the before mentioned submersible filters along with the SunSun CUP series true UV Sterilizers that are a self contained filter, pump, and UV clarifier (these are mentioned in more depth in the UV section of this article). This would make for a simple "plug & play" redundant pond filter system for most ponds under 750 gallons
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.
This article about Aquarium filter media can also be applied to ponds:
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.
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.
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.
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).
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;
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 best is 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.
With either of these filters, I would strongly recommend a DIY Veggie/Bog filter to provide nitrate removal via plant roots end de-nitrification.
The picture to the left demonstrates a DIY barrel type pond filter that could be built by anyone with reasonable DIY abilities.
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.
For information about different filter media that can be used in your pond filter, please visit this article:
 PLANT FILTRATION (Often called Veggie or Bog 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.
I will often place this plant/bog 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.
The key is also water movement along with a good media (Volcanic Rock is preferred) around the roots/tubors. While the flow does not need to be 'fast', there should be a definite flow of water through this Veggie/Bog filter. Often a lack of flow and use of a good media such as volcanic rock is why some Plant/Bog filters fail to work very well and algae such as hair algae will then grow out of control.
Other methods include separate veggie filters in containers or pools. I am not as fond of this method for the reasons above, however these can work.
Here is a video showing how the proper construction of an "in-pond" Bog/Veggie Filter coupled with a TRUE UV Sterilizer (in this case the TMC Pond Advantage, do not use an economy UV) can make a big difference in just a couple of days:
FOR MY FULL VEGGIE FILTER ARTICLE, please visit this link:
This article includes much more information on this subject, as well as links to resources for bog plants and similar.
For those who read this, please note that my emphasis of the use of Veggie filters is not driven by financial gain, as 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.
The picture above/right is of a pond with relatively new Veggie/Bog filter where water flow was also recently added improving the results.
 UV STERILIZATION (& Algae Control):
Although not always necessary in a well planted, well shaded, well filtered aquarium; these devices are still very useful.
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!
It is also noteworthy that the same UV or even a lessor UV may clear a pond one season and not the next; this is quite common as a pond matures, in particular in a pond with inadequate filtration!
Another common mistake is to simply run even an effective true UV such as the AAP/TMC Pond Advantage, AAP Pro Clear Pond, or Emperor from just a water pump with no pre-filtration prior to entering the UV Sterilizer. This increases water turbidity considerably and thus lowers UVC effectiveness also considerably. Simply placing your water pump in a bed of volcanic rock can often work as a pre-filter, so can a Hydro Pond Sponge Pre-Filter.
Further Reference: UV Sterilization; Water Turbidity
As well longer periods or never clarifying can simply be due to an inadequate UV 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 AAP/TMC Pro Clear UV30/UV55 can go to over 70 gph per watt).
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.
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;
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.
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.
You can also simply add a separate lower rate pump just for your Pond 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.
Often it is difficult to determine the flow rates of larger high pressure pond/pool pumps rated in HP (horse power) rather than flow rates that are occasionally used in larger ponds.
This diagram can help determine flow rates at certain head pressures if you own such a pump (please click to enlarge). It is noteworthy that these pumps in 1/2 HP or higher do not even loose flow to head pressure until after 12 feet of head.
Here are a few solutions if the flow is too slow through your UV Sterilizer:
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.
For Small Ponds, self contained Internal/Submersible UV Sterilizers are growing in popularity, however I would caution prospective buyers that the first generation models have problems with electrical failure and are not efficient.
Product Resource: Submersible UV Sterilizer Pump, Filter
I would also point out that while these UV/Filters do provide some filtration, this is intended primarily for pre-filtration prior to water entering the UV-C chamber.
For larger ponds (over 2000 gallons) often placing two UV Sterilizers such as two AAP/Terminator 36 Watt UV will be more economical than one larger UV Sterilizer as when used with separate pumps, the flow pattern is often better, therefore the pond "turnover rate" (how often the entire pond water passes through the UV Clarifier) is generally slightly higher than one unit of say 75 watts that often costs more than double the price as well.
Better is a unit with long exposure such as the before mentioned TMC Professional 110 Watt UV Clarifier or a couple of TMC Pro Clear UV30s as compared a Smart HO Two-Lamp 100 Watt UV Sterilizer.
Or as another example, two TMC Pond Advantage Premium 25 Watt UV Sterilizeras compared to one Emperor 50 Watt UV.
Another important consideration with the use of ANY UV Sterilizer for outdoor pond use is protection from direct weather exposure.
If you have problems with a new UV Bulb firing, please see this video and/or read this article:
Finally, while I recommend a UV Sterilizer/Clarifier for most ponds, I find that many pond keepers are too dependent upon this device where as if the UV ceases to function the pond immediately turns pea soup green.
In my experience this indicates a pond that also is in need of better filtration, as the UV Clarifier should be a compliment to good filtration, not make up for poor filtration. The Veggie Filter I suggested earlier is a good idea, or simply adding more filters if your pond has some filtration, but your current filtration is not adequate.
Further Reference: DIY Pond Veggie Filters
 POND ALGAE (Green Water and Blanket weed)
For MUCH more about the control, prevention and treatment of pond algae, please read this article:
Also see this article for information specific to Cyanobacteria:
Cyanobacteria in Ponds, Aquariums
In a healthy pond, with a properly functioning nitrogen cycle, water changes can be minimal. I still recommend a water change of 10-20% per month on a healthy, fully functional pond. In a newer pond larger and more frequent changes may be necessary.
If a lot of leaves fall to the bottom of the pond vacuuming them or raking them out is important to prevent organic buildup.
Water changes also will help with pH and KH if your tap or well water is slightly alkaline and has a KH above 80 ppm.
Your pond filter should also be part of your pond cleaning schedule. With a pressurized filter such as a Pressurized Pond Filter, I recommend cleaning and rinsing once per month during pond season or more often if the flow rate slows down.
Veggie Filters should cleaned and trimmed at least once per season.
 POND CYCLING:
Generally speaking this process is about 99% the same as aquarium cycling, so I would strongly recommend reading this excellent article:
I would add in addition to this article that the process of cycling in a pond takes 6-8 weeks in warm months, but cooler temperatures such as a pond under 60 F can delay this process.
 POND CARE BIOLOGICAL PRODUCTS
For sludge build up products such as SeaChem Pond Stability, Natural Environmental Beneficial Bacteria, or Microbe-lift are useful for aiding in the breakdown of sludge and other organic mulm through the action of bacteria and enzymes.
 POND CHEMISTRY (GH, KH, etc..);
This is important not just for fish health, but also for algae control as well.
A good electrolyte level is an important aspect of pond chemistry many miss
This is maintained by a constant supply of mineral positive ions (Cations) will also help maintain a good Redox which in turn aids in water clarity, not to mention the very important aspect of good osmotic function in fish for long term health.
If your GH is low this can be a problem (with a stable pH) during the hours of the day when photosynthesis is high, even with an adequate KH.
Products such as Wonder Shells (or Sea-Lab for larger ponds) can help with supplying essential mineral cations as well as oxidative stress/poor osmoregulation, ammonia, & stress from transfer.
For more about how this affects algae, please follow this article:
For more about Alkalinity and hardness in ponds, please read this outside resource:
Generally most Pond Fish such as Koi and Goldfish like a higher ph of about 7.8 (although a pH in the range of 6.8 to 8.0 is often acceptable). A well planted stable pond usually does not have problems with too high or too low a pH.
Product Resource: Marine Buffer; Excellent for Pond Use
For too high a pH (rare), these are cost effective ways in a pond:
 POND FOAM:
Foam around waterfalls and other water features is not uncommon, however if this is a persistent problem, there may be other issues at play in your pond.
For minor problems, especially foam that occurs only around water features, products such as Jungles No More Foam can be useful for blocking the waters ability to foam.
Feeding a quality diet can be beneficial for growth, breeding, color, and even the environment as there is less nitrogenous waste to add to the water column.
This is a broad subject that is beyond the scope of this article, so I would suggest reading more specific articles, here are a few suggestions:
This is far a complete list, however many more can found in our Aquatic Information drop down list in the header bar or at Aquarium/Pond Answers.
One important point I will make and that is the importance of changing water (at least 25%) prior to every single treatment.
The reason is that ponds in particular generally have a high content of dissolved organics, floating algae or similar bio substances, much more so than the average aquarium. These organics will absorb many treatments, especially chemical treatments such as those that contain Malachite Green (such as Quick Cure, which is a very effective pond treatment of many small pond parasites).
By changing water first, this allows for more medications to be delivered to the pathogens causing disease, as well this will generally improve water conditions which in turn helps the fish fight off the infections/infestation better. This can also lower the amount of medication that might be needed to treat your pond as well.
I recommend this water change prior to any and all treatments.
A few suggested pond use treatment products that are biologically safe when used correctly, in particular for prevention are:
 WINTER POND CARE;
It is important in winter to keep at least a small section of your pond open for proper exchange of gasses (O2, CO2), if water can still flow into the pond through a water or aeration device, that will work. A minimum depth of 24” (deeper in climates where soil temperatures drop below 32 F) will provide enough water space under the ice for fish to hibernate (even in the coldest climates, ice will really extend more than 6-8”).However if you live in an area of hard freezes, you may need heaters or a device such as this Pond Master Deicer:
If an aquarium heater is adapted to your pond, make sure that there is circulation near the heater and keep in mind that all you are attempting to do is raise the temperature above freezing, so generally only about 1/2 watt per gallon is all that is necessary for most ponds to keep above freezing (assuming adequate circulation).
For example, a 300 Watt Heater should work for most 600 gallon winter ponds (unless you live in the arctic circle). Make sure to protect the heater from fish or turtles that may break the heater using a cinder block, brick, large rocks, etc.
For a smaller 100-200 gallon pond, such as patio or prefab pond, generally a 200 Watt or smaller heater is all that is necessary to take the edge off the cold.
Product Resource: Via Aqua Premium Quartz Heaters
An aeration device or pump placed about midway from the surface/bottom that circulates upward generally will keep an area of the pond surface free of ice and allow proper gas exchange. In deep ponds over 5-6 feet (1.75 -2 meters), thermal layering, called thermoclines, may exist. This acts as sort of an “inversion layer” similar to how smog gets trapped in the air in Los Angeles. This traps CO2 and Hydrogen Sulfide near the bottom which is dangerous to fish and in this case you need to add water pumps or aeration devices at the bottom.
*Million Air & SunSun Air Pumps
*Pond & Aquarium Pumps
Sometimes removal of fish in the winter is also necessary when the pond is very shallow (under 18-24 inches). I recommend avoiding this if at all possible with larger mature fish as this can injure and often cause more stress than simply improving your pond to deal with winter conditions.
 POND BOTTOM, CONSTRUCTION, REPAIR, SUBSTRATE:
Construction and make up of your pond can be done in three different ways (and there is no one best way; the best way fits your pond size needs, climate and budget).
It is not unusual for a pond to have a leak from either time, poor construction, weather damage, animal damage or "you name it".
 SPRING FED POND (Also water level maintenance);
If you live in an area of natural springs or have creek flowing nearby, this can make for a very healthy, clear and natural pond.
Another method for adding water simply is a float valve. These will add water due to evaporation or loss of water by other means and can even be used with flow through system to automatically regulate water level. Here is a picture of such a float valve by Hagen (Laguna).
 KOI, GOLDFISH, ROSY-RED FATHEADS & GOLDEN/BLUE ORFE;
The Golden Orfe (& Blue), is suitable for ponds. It can grow up to 2.5 feet but usually stays near 1.5 feet. It is a long, slender, bullet-shaped, schooling, orange fish often with black dots on its head and back. Orfes are native to Europe and were derived from the ide which is a silver predator. They need lots of room generally live 10 20 years, however this has not been established.
The Fathead Minnow and Rosy Red Minnow are popular fish for ponds and even aquariums. These small graceful fish do well in similar water conditions as Koi, Goldfish, and Orfe which is higher GH and a pH between 7-8, and prefer temperatures between 50 75 (10-24 C), although they can survive between 33- 100 (1- 38 C).
 POND PREDATORS:
I found Heron decoys such as this one by Hagen: worked well at not only scaring away Herons, but other predatory birds as well such as Cormorants, Owls, etc. (I might note that these decoys do NOT work in breeding season which early March 'til late May where they actually may attract Herons!). I also suggest moving the decoy around as Herons can quickly learn that this is a fake Heron.
This Alligator decoy is another Heron deterrent that others have used successfully (I have not used this method myself, so I cannot personally vouch for it, but it certainly seems like a good idea and I trust those who have claimed to use it successfully).
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