Umm do not do a 100% water change, that is ridiculous. I had the same problem and I just had a HOB filter. I would invest in a canister if you can (or a UV sterilizer) and throw a couple of the fluval polishing pads in there. Change them every couple days until the water is clear. Worked for me anyways. I would even say never do more than a 30% water change, 50% is too much!