berfore adding any chemicals toa system that does not require it, you can probably fix it by altering your system to be a more natural ecosystem......In that, filtration and flow are going to be your best paths when it comes to fixing this. Chemical additions are not what I would consider a viable longterm option. In your case, flow is my number one guess, overintroduction of unwanted nutrients (phosphate, etc) is a close second, and increasing your flow and natural filtration will probably solve the problem....if not, you are adding nutrients and need to monitor the water for changes, and feedings to consumption ratio etc. Good Luck.