weeble

From the sound of it, your pond has not completed its 'break in' cycle. Have your pond and tap water tested for nitrites, nitrates, ammonia, and phosphates if possible. Ammonia and nitrites are somewhat toxic to fish, so try to not let these levels get high. Sometimes these nutrients come from the tap water (in which case flushing out the pond will make the problem worse), sometimes from run-off from fertilizer on the lawn, or sometimes from fish and critters.

Ponds often go through a phase where algae goes crazy because the nitrite and ammonia feed algae quite well. If you let the bacteria grow that break the ammonia and nitrite down, you will probably find the algae decreases. By changing your water and cleaning out the pond, you can kill this bacteria, which grows on surfaces like gravel or filter media or even the pondliner. This slows down the 'cycling' or even re-sets it so it starts all over again. This bacteria helps keep the pond clear by converting the ammonia and nitrite to nitrate, which is harder for algae to use for growth.

A UV filter will help because it kills off the free-floating algae, but NOT the bacteria attached to gravel and such. There are several theories as to why barley straw works, but it seems to help keep algae growth down.

I'd suggest NOT flushing the pond next time it gets green, just let it cycle. Try the barley straw, but give it time- it can take several weeks for the barley straw, and the 'break-in cycle' takes a month or so at room temperature. UV filters will work faster, but they are expensive.

Maryjane
aka Weeble

Oh yeah, tadpoles eat algae

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