This is the 2nd year with our little garden pond. It is an above ground pond of 425 gallons.
We had some green water issues the first season as the pond was becoming established, but now that a healthy coating of algae has settled in on the bottom and sides, the water has been clear and the parameters have been good, with the exception of pH...more on that in a bit. This season I have been battling string algae. I am removing it by hand almost every other day. I know string algae is not an indication of unhealthy water, but it is not very pleasing to look at. (Damn, that stuff grows fast!
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The contents in the pond are 8 sarassa comet goldfish between 3-6 inches, a dwarf water lily, a dwarf cattail, 3 water hyacinths and 3 water lettuce. Originally, I placed the cattail and water lily on upended concrete blocks (cinder blocks I bought at Lowes). I had read that concrete will not harm the fish, BUT lately I have been doing a lot of reading related to string algae and found out that untreated concrete can raise pH and phosphate levels which are favorable to string algae growth because they raise the magnesium and calcium levels of the pond. The phosphate in the water is low, but the pH is off the chart!...above 9.0. Probably more like a 10, but my chart only goes up to 9.0. This high pH level does not seem to adversely affected my fish (yet) since I have seen no signs of problems in them. Yesterday, I decided to remove the concrete blocks and replaced them with one small plastic table to raise up the lily and cattail. I also did a partial water change...about 50 gallons...to start gradually bringing the pH level down. When I removed the cinder blocks they had small, hard, irregular bumps on them...like mineral deposits.
The water I am topping off my pond with has a low pH of about 6.4. I bypass the water filtration in my house for my pond and garden water.
Also, I only feed the fish a "treat" of a few small pellets each about twice a week which they gobble down within seconds, since they are very capable of living off the healthy algae, so they are not being overfed leading to food waste in the water.
Just wondering if any of you have experience with combating string algae, and am I on the right track with what steps I have taken so far?
