Posted 04-16-2003 at 04:16:26
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The algae grows because of an availability of excess nitrogen in the water. There are algicides that work, but they are not long-lasting--the algae will grow right back as soon as the killer dissipates.
So the best solution is long-term, low maintenance way to remove the nitrogen. We have had goldfish/koi ponds for many years. In the spring, there is always some algae bloom, but you can minimize it and the rest of the year you will have very clear water.
First off, if you have fish in there, don't feed them quite as much as you are...the feed and poop are key sources of nitrogen. Fish also help by eating algae, although their waste has to be removed, too or else the algae will just keep growing back.
Growing some pond plants helps a lot, too. Water hyacynth are probably the best, although you have to occasionally take them out and compost them (don't let them get into a "real" pond or they'll take over...very invasive). But they'll clear a pond in a couple of weeks, and the roots also provide food for fish, too.
Filtering also helps. We use a recirculating pump through a biological filter, which is basically a barrel full of gravel, course sand, and a couple of polymer pads that bacteria grow in...the bacteria eat the nitrogen and help keep everything (fish and plants) healthy. Depending on your setup, the filter takes very little care. I pre-filter the pump with a sack full of straw...have used barley straw (*straw* not *hay*!!) and it works well, but so does any other kind of straw as long as it is long-stranded. Have tried some chopped-up straw and found it clumps quickly. Just tossing it in the pond may work, too, but I suspect it won't be near as fast or effective as having the water flow through it. You have to replace the straw periodically, depending on the weather and flow rates.
If you've got any other questions, please ask...feel free to shoot me an email, just put "Country Life" or something like that in the subject, cuz I delete most everything from folks I don't know--am sick of spam!
I'll put my email below, just replace "(at)" with the @ and it'll work just fine.