I'm still old school, I just pull it out manually. The good news in my pond is that when the string algae appears, the water clears up.

There's 2 things that seem to keep string algae happy, high nutrient levels and good sunlight.

I'm with PK. Waterbug_Guy has done some studies that suggest that string algae competes with other algaes and prevents their growth. The string algae doesn't actually turn your pond green like single cell algae types; and the string stuff is easy to pull out. As I have mentioned elsewhere, I use it as a cleaning method by pulling the stuff out along with attached crud that has been filtered out by the string algae.

Actually the really easy way to get rid of string algae is to change the way you look at maintaining your pond... The top post on this link explains it better. .... The Lazy Solution to Algae in Ponds

Here's what some people miss when dealing with string algae. If you kill it chemically, you still need to get it out of the pond. If you leave it in the pond dead and dying you are only adding more nutrients to the pond, which only starts the cycle all over again. So either you pull it out before you treat the pond or you pull it out after you treat the pond - either way you're pulling it out. So why not just pull it out and skip the chemical treatment all together? (Not a fan of chemical algaecides myself. I think they are killing lots of microscopic, important pond things that you can't see.)

Algae is a plant. Plants are good for ponds. It's letting you know there's something in your pond that needs to be addressed. So it's a symptom, but it's not a real problem. Treat the problem (or wait for other factors to kick in, like plants to start growing) and the symptom will resolve itself.