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!
OK, I know that you said you do not want to use chemicals, but I am amazed that nobody has mentioned Cloverleaf Blanket answer. I was recommended this last year and oh my gosh, the stuff is AMAZING! From what I have read, it is not chemicals as such, but enzymes? Either way, I literally do two treatments at the beginning of summer and it wipes it out completely leaving crystal clear water. I only seemed to get blanket weed this year from buying in a couple of plants. It seriously is amazing stuff!
NJS1982 wrote: I am amazed that nobody has mentioned Cloverleaf Blanket answer.
I can answer that (Why no one has suggested it before) No one here uses it.
If you do some research on it you will find its like most "miracle cures" some say it works some say it doesn't. Also to be noted is the amount of zinc that is in the product, too much and it is lethal to fish.
Blanket weed is an odd thing, you can not have it for years then all of a sudden, you have loads of it. To date no one has published a 100% way to get rid of it that is safe for fish etc.
Good quality costs. Bear this in mind before you start.
Sorry if my reply is NOT want you want to hear, but what I have said is true.
I was told about it via my Dad's friend who has pretty much converted his garden into an area of multiple koi ponds (but with no plants?!).
I had tried a few things before to get rid of the blanket weed and spent hours dragging the stuff out (and freaking out my old housemate as she hated the look of the stuff!).
I am rubbish at working out the measurements for it (and I work in finance!) so always rely on my other half, who is a Quantity Surveyor to tell me how much to put in the watering can!
Surprised about the zinc; will keep an eye on that, but as I have said, never had any ill effects at all, my fish are very healthy and I still have lots of frogs, toads and newts lurking around. It would be interesting to see if anyone has had any bad experiences using it?