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! )

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?

Jim how many gallons is the pond, goldfish will eat string algae, I would stop feeding them for awhile

http://aquariumalgae.blogspot....

The pond is 425 gallons. I used to feed them every day last year. This year I only give them a "treat" about twice a week that they gobble down in a few seconds. I''ll stop feeding them altogether.

Well, I removed the 2 concrete blocks...typical "cinder" blocks...16 x 8 x 8 with the 3 openings. Within a day or two, I noticed I had less string algae and was not cleaning it out. In fact, the string algae on the walls began to diminish. I imagine the sarassa's are eating it. The string algae is well under control now after removing the 2 concrete "cinder" blocks. I guess the chemical reaction was creating the string algae as confirmed in my research.

Interesting about the cinder blocks. I don't have trouble per se with algae of any type seeing how my ponds only receive morning sun. All ponds have cinder block and only 1 pond has sting algae and it is growing around the pump/fountain leaving the cinder blocks alone. But I am glad you found your culprit. I might take the pump out and give it a good wash.

The string algae was not growing just on the cinder blocks but throughout the pond. Removing them and doing a 20% water change lowered the phosphates and pH and subsequent water testing indicates both are within more normal ranges now. The amount of string algae growing was just too much for the fish to consume. I am no longer cleaning string algae that was throughout the water, and the fish have taken care of it on the surfaces to the point it is well under control and does not have to be manually removed any longer.