The plain truth of the matter is that ponds require regular maintenance. Emphasize "regular". Mother Nature may take care of her own lakes and streams, but a human-built water garden requires frequent human intervention. This means that you, the gardener, must keep the water clean and free of bad chemicals, the plants pruned and in bounds, the fish fed (but not overfed) and the water level consistent. Let's take these tasks in order.
First-the water quality. Pond water will not be crystal clear and that's OK. Some algae is normal and good for your fish. You can't really improve your water quality by adding fresh city tap water. Work with the water in your pond and avoid doing complete water changes if you can. The chlorines and chloramines of our potable water system can harm your fish if their levels get too high. Likewise, the chemicals leaching from new concrete and lawn products like weed and feed can wreak havoc with your plants and fish. Get a test kit and use it to make sure that your water has proper pH, does not show high levels of ammonia (decay byproduct) or chlorine.
It's a problem when you have green water so murky that you can't see the fish or the underwater plants. This occurs when your pond gets too many nutrients and too much sunlight on the surface. Where do the nutrients come from? Fish waste, excess fish food, excess fertilizers and decomposing plant material all provide nitrogen that feeds algae. So-don't overfeed your fish and don't overstock your pond with fish. Don't feed at all when the temperature falls below 50, as it is beginning to do in our cooler October nights.
If the fish are hungry, they will eat more algae! Clean up the organic matter that drifts into your pond and prune away the decaying tops of plants that have finished their life cycle. You can put nets over the pond to catch autumn leaves that drift into your water garden. Overhanging trees may look romantic but they can be a real headache as they drop leaves and catkins into the water. During summer, skim the leaves regularly so they don't sink to the bottom and make sludge.
A biological filter system is your best route to healthy water. When connected to a recirculating pump, it can clear a lot of the bad things from your pond. Size is critical-the larger the better in most cases. The action of a bio-filter takes place on the surfaces exposed to bacteria-gravel provides more surface area than one large rock. Lava rock is frequently recommended as filter box filler. There are plastic foams and polyfiber filter materials also available. And, most important, there are bacterial inoculants you can buy to add nitrifying bacteria to the water. Once these have settled onto your gravel or fiber, they eat the ammonia produced by fish waste and decayed vegetation. This is what you want to happen.
My current filter requires cleaning about every other day. Filimentous algae and other debris clog the intake screen and must be removed. This isn't hard to do-it just has to be done regularly and that's where I fall down. I can't seem to stick to the schedule. My answer is to build a bigger filter box-that should hold me longer. And I have increased my skimming. I got a larger net on a longer pole to keep the floating leaves and blown-in junk from sinking to the bottom. I just have to do this more often.
Now that it's fall, I will drain a portion of the water garden and vacuum the sludge from the bottom with my shop vac. This is a tedious process. The fish must be caught and transferred to a kiddie pool full of pond water, the pots of plants removed, the water drained (but it makes great irrigation water for the perennial beds) and the sides of the pond scrubbed clean. No soap or detergent, please! Elbow grease is what is required. Then, after rinsing, when the pond is refilled, I will have to start the balancing act all over again. New water is harder to deal with than seasoned, veteran water. But if I go into winter with a cleaner pond, my fish and my plants will be healthier and prettier when temperatures rise again in the spring.
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