That is curious though I guess there can be a cold weather strain if string algae.

We have algae that not only survives - it seems to thrive in the cold weather. I'm grateful for it as I assume it's doing the same thing that algae does in the warner weather - consuming any nutrients in the water, helping to keep the pond ecology balanced.

Hey guys, I have had the similar problem years past. Remember algae is at the bottom of the food chain. All year your plants have been eating up the nutrients in the water. Well now, with plants being dormant, algae takes over.
I know there is allot of hype on Iongen. However since I added, I've had no problems. Granted I take it out for the winter, but it seems to clear the water. I've heard bad things about hooking it directly up to your flow line. I personally like just hanging it in the skimmer box.
For those with smaller ponds, not to worry. I've noticed Lisak believes in keeping a pond naturally balanced. It will help your pond ecological system. The only thing is you may have a little more clean up in the spring with a pea green pond.

Craig