Springtime Pond Calls by Dr. Greg Lutz, Aquaculture Specialist
This time of year you may get a lot of calls about floating scum in ponds – usually the problem is filamentous algae. Filamentous algae generally prefers cooler temperatures, and the problem usually begins during the winter months when abrupt temperature changes cause ponds to turn clear. This lets the sunlight reach the pond bottom, where the filamentous algae starts growing in mats. As water temperatures warm during the spring, the filamentous algae becomes stressed and sloughs off, floating to the surface. In mild cases, it’s just unsightly. In moderate cases, it can interfere with fishing, and in severe cases it can cover enough of the pond surface to cause oxygen problems. As the floating algae is exposed to direct sunlight it usually breaks down over several weeks but sometimes the problem can go on for much longer periods.
The most practical way for most of our clientele to deal with filamentous algae is to kill it (or hasten its death) with copper sulfate crystals. Unfortunately, if the pond water is very soft, copper sulfate can be toxic to fish. If it’s very hard, copper sulfate can precipitate out of the water before it does much good. Nonetheless, in most cases it works pretty well. And it makes the pond owner feel like he or she is doing something to fix the problem.
An important rule of thumb for applying copper sulfate crystals is to have the pond owner limit themself to 5 pounds of crystals per SURFACE acre, followed 7 or 8 days later by another treatment. They should broadcast the crystals over the most problematic areas – but once they have used 5 pounds per acre, they must stop and then wait 7 or 8 days and make another treatment in an area they weren’t able to get to the first time. This can be repeated until the problem is under control. So, a 3 acre pond would get 15 pounds of crystals per treatment, and a 1/2 acre pond would get 2.5 pounds per treatment. Pond depth is not a consideration, especially since the goal is to get the crystals directly onto the floating mats of algae. Hand and eye protection and appropriate clothing should be recommended when the crystals are being applied. In a few cases, the filamentous algae may be resistant to copper. And, finally, there is always a chance that oxygen problems can occur when killing vegetation, and pond owners must be made aware of this possibility. But, when people stick with this 5 pounds per acre limit I have never seen anyone cause a fish kill.
Also, we see lots of problems with diseases and fish kills this time of year – here is a page to get your clientele started in sorting out what their problems may be and how to respond to them. http://www.lsuagcenter.com/en/crops_livestock/aquaculture/recreational_ponds/Frequently+Asked+Questions/Springtime+Problems.htm
And as always, if you get calls about ponds and it’s a situation where there is no obvious recommendation, feel free to put them in touch with me directly.
Hope this info helps. GL