nitrate/phosphate ratio and cyanobacteria

[Mareva]

I know we've had a couple of thread about cyanobacteria before, but I can't find what I need!
I've had a problem with cyanobacteria for a while. I changed quite a few things, added plants and made sur no overfeeding occured and all. I had it disapear once with closing the light for 5 days, but it just keeps coming back and I think it's a low light variant because closing the light doesn't work anymore!! Then I saw Troender posting this table where it said that low nitrates and some phosphate were perfect for cyanobacteria.

Well, my nitrates just happen to be below 2 at all times! And I don't have a phosphate test, but obviously there must be some in my tank! So, where do phosphate come from in a tank? How can I control it? How can I increase slightly my nitrates? I tried going from 50% WC to 25% WC weekly, but there's no change, I bet my plants are all eating the nitrates! So any idea how I can change that ratio so I can finaly get rid of the darn thing?

[Troender]

I've heard of one trick, but I would be careful if I had to use it in a puffer tank. Take some of the cyanobacteria and put it in the filter. There it will die, and the nitrate be released into the tank. The new nitrate will change the phosphate/nitrate ratio, and hopefully the cyanobacteria will go away. But as puffers are so sensitive to nitrate, I would be very, very careful doing this. Actually I have a tank with the same problem. Maybe I should test this myself?

[Mareva]

The green stuff is actualy growing on the filter media bag!!! It doesn't seem to kill it! I'll try to see what else I can find... lets keep in touch about this!