If there is excessive algae in a garden pond, it may mean:
There are not enough plants to keep algae from gobbling up all the oxygen and nutrients.
Too much sunlight reaching underwater; add floating plants like water lilies to help shade the bottom.
Too many nutrients; use soil especially made for an aquatic garden and slow-release aquatic plant food.
If pond water is cloudy and brown, it may mean:
Pump and Filter are not working efficiently. Clean the pond filter often. Foam filters must be removed, washed with water and liquid detergent. Cartridge filters should be hosed down with a strong stream.
When pond has leaves and plant debris, it means:
Dead leaves are from nearby trees. Skimp the pond surface often with a net on a long pole. If there are several trees close to the pond, catch leaves that fall by stretching garden netting all the way across the pond surface and anchoring it on both sides.
There are dead leaves from pond plants. Examine pond plants and remove any yellowing or dying leaves.
When floating plants appear unhealthy:
When a plant such as a water lily has excessive leaf growth, with leaves rising above the water surface, it probably isn't getting enough nutrients from its container to promote blooming. Remove the plant from the container, divide it and put half of it in a second container elsewhere in the pond.
When fish appears unhealthy or are dying, it means:
They lack oxygen. Add more submerged oxygenating plants like duckweed and eelgrass, which will help reduce the amount of algae.
There are too many fish. There should be 1 to 2 inches of fish length per square foot of pond.
Too much chlorine or chloramines in the water can be deadly to fish. Test the pond with kits and use commercial treatments to reduce them to a safe level.
If plants or fish freeze under ice during the winter:
Move fish and container plants that are not winter-hardy to a sheltered place. Place a small floating ball in the pond to keep part of the surface clear of ice during frosty weather, so that gases in the water can disperse.
When underwater plants are dense and matted:
Submerged plants have excessively grown. Plants need to be divided.
When pond water level is low:
In the summer, water evaporates. Check pond water daily and add water if needed.
There is a leak in pond liner or fiberglass form. Repair any tears in liner with patch from a scrap of liner. Fix cracks in a with a fiberglass-repair kit.
When toads, snails, and newts settle in:
If a population explosion threatens at spawning time, collect excess spawn and transfer either to a permitting neighbors pond or to a natural country ponds. Consult a professional water gardener before taking any action you don't want to spread diseases or catch one.