BIG WATER CHANGE

Agree with all of the above.. Since you are just having this issue and switching to ro/di something you may want to look into like Amp said is a phosphate remover.. Something that works great removing all kinds of gunk is the PolyFilter pad. It doesn't leach anything back into your system, it traps all kinds of contaminants you just need to place it in someplace that has a good flow through it. You could actually place it in your canister filter if you have it already. I have used one in my sump when I was having algae issues.

It locks up phosphates, ammonia, waste etc etc etc.. Great product. They are a little pricey but if you don't plan on buying something like a phosban reactor and media or something along those lines it is a good fix for the short term.
 
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