Schuylkill River Park Community Garden

Creating a Successful Water Feature

A water feature can be a great addition to any plot, ranging from a full blow pond ecosystem to a small solar fountain. If you plan to keep a water feature, it is very important to prevent it from becoming a haven for mosquito larva. Mosquitoes are attracted to any vessel of standing water and will colonize your water feature unless procedures are put in place to prevent their development. The two most common prevention techniques are: 1) frequent emptying of the vessel and replacement with fresh water; 2) adding some organism (e.g., goldfish) that eat mosquito larva. In the former technique the water feature is maintained as a “sterile” environment that is not intended to support plants or any other life. In the latter technique, an ecosystem is developed that allows fish and plant life to exist.

It is the latter technique, building a contained ecosystem, to which the remainder of this article is devoted. The first consideration in setting up a pond is your water source, which will most likely be Philadelphia Tap Water. Tap water in almost all municipalities contains chlorine or chloramines (a combination of chlorine and ammonia) used by water treatment facilities as a disinfectant. Philadelphia uses chloramines as their tap water disinfectant. Both chlorine and chloramines can be deadly to fish or other aquatic life in the pond, in some cases by direct toxicity but in most instances the disinfectants prevent the formation of bacteria that would otherwise break down fish wastes into non-toxic organic compounds. In absence of these bacteria, eventually fish waste reaches toxic levels. Therefore the removal of chlorine and chloramines is essential before adding any aquatic life to the pond. Although chlorine removal can be facilitated by allowing the pond water to stand and off-gas for a few days, the removal of chloramines is more challenging and is generally best realized by adding a product to facilitate its removal (usually containing sodium thiosulfate). A good example of such a product is API Tap Water Conditioner API Stress Coat.

Once your pond is filled and chlorine/chloramines have been removed, it is very important to allow the pond to cycle for a bit before adding any fish. The waste produced by fish and other aquatic life contains ammonia, which is highly toxic once released into the water. “Cycling” a pond or aquarium refers to the build-up of aerobic bacteria that convert ammonia to a less toxic nitrite and ultimately to a low toxicity nitrate. In indoor aquariums this process can take up to 3-4 weeks, but I have always found the process to occur rather quickly (a week or so) in outdoor ponds. You can just wait for this process to occur or you can actively test for ammonia and nitrite using an aquarium test kit. You should see a spike (increase) in ammonia followed by an increase in nitrite. Once the cycle is complete, both of these values will drop to zero (they must be zero) and nitrate will start to increase. At this point, you can slowly add fish. If you add too many fish at a time, the bacterial production will not be able to keep up with the fish waste and you will end up with ammonia and/or nitrite in the pond, which will be deadly to the fish you have just added.

Once you have fish in your pond, nitrate (which is not toxic to fish in relatively low amounts) and phosphate (not toxic to fish) will start to build up in the water. The bacteria that remove nitrate (by conversion to nitrogen gas) will rarely if ever exist in an outdoor pond because they require anaerobic environments. Thus, these compounds, as they build up, must be removed by some other mechanism or eventually they will start to cause problems for your ecosystem. Most notably, both phosphate and nitrate can be considered “plant food” and will eventually fuel massive algae problems in your pond.

A second long-term issue to consider is oxygenation of the pond – because you do not have a filter or other mechanism to create water flow to facilitate diffusion of oxygen into the pond (we have no power!), your fish can eventually become unhealthy and/or die from low oxygen levels. Fortunately, both the issues of increasing nitrate/phosphate and oxygenation can be solved by adding specific aquatic plants to your pond. The plants consume nitrate and phosphate as fuel used in photosynthetic production and, at the same time, use carbon dioxide and release oxygen into the pond. Only a few plants are required as they will multiply rapidly as available phosphate, nitrate, and carbon dioxide allow. Excellent plants for this purpose are Anacharis and Hornwort, which can be purchased from the Pond Megastore as well as from several local retailers that sell pond plants (Waterloo and Albrecht come to mind). Water lilies and other aquatic plants can be helpful as well, but from my experience Anacharis and Hornwort are among the most efficient at oxygenation and nutrient export. I cannot emphasize enough the difference that a few well-selected aquatic plants can make in the quality of your pond ecosystem and in the health of your fish. They will also almost completely eliminate algae by outcompeting it for nutrients.

Now to the question of which fish are best for a water feature in our relatively small (10x10 to 10x20) plots. There is a temptation to add Koi to your water feature, but unless you are prepared to devote 500 gallons or 1,000 gallons to your pond, Koi are not a good idea. They simply grow too large for smaller ponds (12” – 24” in length) – not to mention that they are rather expensive. Good additions are goldfish of almost any variety, including the smaller feeder goldfish that you can purchase at most pet stores for very low prices (12 fish for $3 or something like that) and Bullfrog Tadpoles (also available at most pet stores and online from the Pond Megastore), which consume massive amounts of mosquito larvae. Fish and tadpoles are rather sensitive to sudden changes in temperatures. Once you purchase your fish, be sure to float their bag in your pond for at least one hour to allow slow acclimation to new temperatures before releasing them. Buy some flake or pellet fish food to feed your fish or tadpoles and use this very sparingly, making sure all food is consumed within three minutes. If any food is left after three minutes, you are feeding too much.

A final note on how to actually “construct” your water feature: Both Home Depot and Lowes (as well as other retailers) have pre-formed plastic ponds that can be dug into your plot. Additionally available is pond liner material (although it’s a bit pricey) that can be used to form a pond of any shape. If you plan to leave your fish outside for the winter, be sure that your pond is sufficiently deep to prevent complete freezing of the water – most people suggest around 2 feet deep in Zones 5 or greater (we are Zone 7).

Good luck and have fun with your pond. When considered carefully and executed correctly, water features can make great additions to any plot.