white, cloudy water

Question
My tank (freshwater; 20 gallon) get's cloudy water. I change 1/2 of the water and I use the tetra additive that is claimed to limit water changes for 6 months. Does not work for me. I have a undergravel filter and a Marineland filter on the back (I change the charcoal filter every 2 weeks). It has a wheel that spins with the water.

I thought about getting one of those canister filters and filling it with charcoal. But the charcoal can be expensive and I cannot afford to change the charcoal every week or two.

What do you think I should do. I also tried those water clarifier drops. They got the tiny debris caught better in the filter pad. But this does not get rid of the white.

Answer
Chris,
It could be the under gravel filter. They are very hard to maintain and do not keep the water clean. As for the tetra additive, they do not work, nor do the drops. How long has the tank been set up and was it cycled? It could also be because of the changing of the charcoal. The filter might be trying to recycle every time. Have you tried just rinsing the charcoal in the old water when you do a water change? That is all I do. I do not replace it very often. Try only changing 25% of the water every week instead of half of it. Other than that it could be the filters not working properly. Make sure the water is being pulled in correctly and brought back into the tank.