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Green algae in the water surface

Problems is part six of six in the Ornamental Garden Pools series.

Water Quality Problems

The two most common water quality problems are oxygen depletions and the build-up of toxic nitrogenous wastes.

Oxygen depletions occur because the total amount of plant and animal life has exceeded the carrying capacity of the pool or because of an excessive rate of decomposition. Fish gasping at the surface is almost a sure sign of an oxygen depletion. Aeration, the best management for oxygen depletions, should begin immediately; then the cause of the depletion should be determined.

The other common water quality problem is the accumulation of toxic wastes such as ammonia and nitrites. This problem occurs because of over-feeding, rapid decomposition, or biofiltration failure. When high ammonia or nitrite concentrations are discovered, reduce or stop feeding, flush with good quality water, and check the mechanical or biological filters.

Algae Control

If the algal bloom starts to cut down on visibility, the natural tendency is to treat with herbicides. This is not recommended as it can easily kill fish if the herbicide is not applied properly, or if the decaying algae depletes oxygen. Herbicides may also kill the decorative aquatic plants in the pool. A heavy algal bloom is usually a sign that the pool contains too many nutrients derived from fish wastes, uneaten feed, or over-fertilization. To treat the problem, you may want to flush the pool with fresh water, reduce feeding or fertilization, add additional aquatic plants or nitrifying bacteria, or reduce the number of fish in the pool.

Controlling Fish Reproduction

Another common problem in ornamental pools is controlling fish reproduction. Over-populating the pool with fish will generally limit fish growth, reduce water quality, and jeopardize the overall health of all the fish. Usually the eggs or fry will be eaten by fish or aquatic insects. But, even if only a few survive, the pool will slowly become over-populated. One biological control method is to stock one sunfish (bluegill). Sunfish are voracious and aggressive enough to eat all eggs and fry in most pools.

Fish Diseases

Disease strikes most pools at some time and is almost always preceded by stress on the fish. Stress has a wide variety of causes. Some signs of stress, disease, or parasites are easy to spot and watching for them should become a part of your pool maintenance routine. The most common signs are a reduction or cessation of feeding, piping (sucking air at the surface), flashing (quickly turning sideways and rubbing on objects), whirling, or visible sores and discolorations. There are more than 100 known diseases and parasites that can infect fish. To have a diseased fish diagnosed, you may send a live, diseased specimen to the nearest fish disease lab or contact a veterinarian who has training in fish diseases. “Guidelines for Collecting and Shipping Diseased Fish” by M. P. Masser and Y. J. Brady is available through your county Extension office. Pool owners should be warned that most fish are sacrificed in the diagnostic procedure.

Stress on Fish

Stress is a reaction to unusual conditions. This includes extreme high or low temperatures, rapid temperature or pH changes, high ammonia or nitrite concentrations, low oxygen, high carbon dioxide, crowding, handling, excessive particulates, and poor nutrition. Stress can be reduced through good management, including proper stocking and feeding, careful handling, and maintaining good water quality.

High angle view of man with sons sitting on footpath over pond with fence in backyard

Predators and Other Common Nuisances

Predation by people, birds, raccoons, snakes, and other animals is a problem that cannot be eliminated entirely, but there are some precautions that should be practiced. Fences around the pool may reduce some predation by animals like raccoons and otters. Netting over the pool will discourage birds but will detract from the pool’s beauty.

Turtles eat water lilies and other vegetation and should be removed from the pool. Also be aware that a few toads can lay lots of eggs and the resulting tadpoles can deplete oxygen from the pool. Watch the pool and discourage animal nuisances.

Mosquitoes can be a problem in pools without fish or in pools choked with aquatic plants. If you have a mosquito problem, add fish, remove excess plants and detritus, or add Bacillus thuringiensis (B.t.) to control mosquito larvae.

In conclusion, an ornamental pool provides a wonderful opportunity to enjoy the natural beauty of plants and fish and gain a better understanding of the complexities and interactions of aquatic communities. It also provides an outlet for creative expression in the design of the pool and its surroundings and enables urban dwellers to add a serene, natural environment to their yards.

Ornamental Garden Pools Series

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