Right, it loves cold water. I've had outbreaks of it in some winters, but not in others. When the water gets a little warmer in April-May, it dies. I wonder if the re-emergence of the dark green shag carpet algae hastens the string algae's demise by out competing it for nutrients.
If it gets bad enough, it starts clogging everything up. But I've found
it can be controlled with a little salt >0.15%. I don't try to wipe it out. I just keep it from getting out of hand until spring. Here are my notes on a couple of attempts of different levels of salt. Both efforts were successful.
- Nov-Dec 2010: Added salt to increase from 0.02% to 0.09% in effort to control string algae. After 4 days and not seeing much results, added more salt to increase to 0.16%. After 6 more days, there were lots spots made bare in the deep water. Walls and shallow sunny areas still had some algae.
- Jan-Feb 2016: Over two days, added salt to increase from 0.01% to 0.18%. I netted out the bulk of the long strands just so all that would not die in the pond. After 4 days, the small number of long algae strings that remained were detached and lying on the bottom. About 80% of the sides have large patches of 1/2" short green algae. The other 20% of the sides have gray dead algae.