I'm sure this topic has been covered many times but when I search it I get an error page. After doing my last water change about two days later my tank became a bit cloudy. I left it for another day or so and it got worse. Here's my stats...3 year old 21 gal freshwater, temp 77-79, ph. 7.4 stable, ammonia 0, nitrite, 0, nitrite sits between 10 and 20. I have been doing approx. 25% water changes twice a week for about 4 weeks, before that 40% change once a week, consistantly. Why would my water cloud now?? It so hazy I can just make out my intake on the back of the tank. I did a water change today of about 20% and it looked a bit clear but now 6 hours later, it looks worse again. Whats up with that?? I haven't had cloudy water since I first set up a few years ago!