Hi,
My pond suffers from string algae, and I have tried a number of things to limit its growth, including:
1) An electronic blanket weed controller (a blagdon one).
2) Barley straw
3) Competing plants (mostly elodea crispa).
4) Shade. The pond doesn't get much direct sunlight, maybe 2 hours a day).
5) An aquarium cleaner/scraper (my pond is a raised fibreglass pond, so is is relatively easy to clean the sides).
It was only towards the end of last summer that the string algae got under control and I no longer had to keep cleaning it out. I've had all winter to think about what the magic formula was for the irradication/control of the algae (ponds are almost boring in the winter!), and here are my very amateur thoughts on the five points mentioned above:
1) Electronic controller - meh, who knows: The electronic controller was installed in the spring. It was running for a long time with no obvious effect, so I am not convinced it is doing much.
2) Barley - Good: The instructions say it takes about six weeks to kick in (it needs to start decomposing). I put it in in early summer, and the pond got under control a few months after that.
3) Plants - Good: By mid summer, the lilies were in full leaf, er pad, and the elodea crispa was rampant. There was now plenty of plants competing for the nutrients, which I suspect is the main reason for the good control of the algae.
4) Shade - Unknown: Not a big issue for me I suspect. The shade was the same all year round, and the plants at their peak only covered maybe 2/3 of the surface, so I dont think shade was the tipping point for the algae to get under control.
5) Manual cleaning - Priceless: Before the pond sorted itself out, the algae made the pond look awful without a bit of cleaning every week.
I would hate someone on here to tell me that string algae stops growing towards the end of summer, as that would mean none of my methods had any effect at all!!
This year I already have the barley in place and it's six week period to start having an effect is up next week so I am hoping to notice the difference soon. I have also kept a lot of plants in the pond (it is now a mature pond, rather than being almost new last year). I am already seeing string algae growth, but the plants aren't yet too active and the barley isn't quite ready. Fingers crossed for an easier year this year!