Midwest Pond and Koi Society - Q&A #109

Hi. My pond is approx 3000 gal. I have 1 goldfish, 2 koi, and a shabunkin. I dug the pond just last summer. We used our well water to fill it.

There is not much shade over the pond and it's not really possible to plant anything to shade the pond because it is sitting between two decks. We have had a constant string algae problem even in the winder. We did water changes about every 3 weeks last summer and constantly scraped the side and bottom of the pond with a soft brush. We bought some chemicals to get rid of the algae but had to get a lot of chemical for the size of the pond so we did not continue with it.

I read on the internet that string algae may be due to a high PH and that you could use baking soda to lower the PH. I started doing exactly as the article said. I think it was to add ½ cup of PH and then wait 24 hours and test and add another etc.

I had plants in the pond but they all got gooey and died, they don't stay healthy in the pond. My husband thinks that I shouldn't put plants in the pond because algae forms if I do however I have read that plants actually help to get rid of the algae. Anyway, I convinced my husband to start a pond last spring and now I wish that I hadn't because it is so much trouble.

My major question of course is how do I get rid of the string algae? How long should it take to get rid of it? Should I treat the pond in the winter? Must I figure out some way to shade the pond?

My fish have been very healthy. I have a floating pond heater so it has not been frozen over this winter.

Dear Disappointed,

This is the most frequent complaint that we hear from beginning ponders, and hair algae is indeed a persistant nuisance. It is the natural aquatic response to the combination of phosphate-rich water, ammonia from your fish, and sunlight. Changing any of these parameters will help control your algae problem.

Chemical algaecides do not work, first, because hair algae is extraordinarily resistant to the effects of chemicals, but also because the algae that is killed settles out as a sludgy, unacceptable organic load on your pond. The other problem is that the chemicals are far more toxic to other aquatic plants than they are to hair algae. Your plants died because you poisoned them, and once the chemicals are in, the only way to get rid of them is with a 100% water change.

The water changes you did during the summer last year were great for the fish, but mostly replenished the phosphate load in the water, a common problem with well water, worsening the algae problem.

Sodium bicarbonate does not "lower the pH". pH is a measurement of acidity or alkalinity of the water, and acid levels are numbers *below* pH 7. Sodium bicarbonate does not directly affect the pH, it actually increases the stability of the existing pH by adding buffering capacity to the pond. Good for the fish, no effect on the hair algae.(see "Who's on pHirst?" in the Articles section of our website).

As far as plants are concerned, your husband could not be more wrong. A robust collection of water lilies, lotus and pond marginals will go a long way towards solving your algae problem, by soaking up some of the ammonia and also , in the case of the lilies and lotuses, shading the water. Get the last of those chemicals out of there and replant!

Any shade you can supply to the pond would be a good thing. If you can't plant, then an arbor over the pond supporting shade cloth would work.

String algae also loves stagnant water. Look at your pond's water circulating system and look in your pond for "dead zones" where the water does not move. Find a way to clear these up.

Armored catfish (Plecostemus) love hair algae, and will also help, but are tropicals and must be wintered over indoors.

If you can get your plants up and growing (and upgrade your filtration to remove more ammonia quicker), the hair algae will not have a chance to be the nuisance it currently is. Every backyard ponder deals with it every year, and all of us use the "brush-on-a-stick" method for overall control. It's a part of the hobby.

Bob Passovoy
President
MPKS