I am experiencing the same problem in my 29 gallon tank. I have recently added quite a few plants (moneywort, wisteria, java fern & another that I can't remember the name of) and it has improved some but not much. The plants do not appear to be growing very fast although I understand some don't (moneywort). Part of that is because I have only been purning my lights about 6 hours a day to try to combat the cyano. It was growing so fast you could almost see it. I do not have a phosphate test kit as I can't find one any where locally. Is that worth the price to order off the internet? Also, will adding CO2 help?