Canister filters are fine, but not for smaller tanks. Your Eheim is designed for a much larger tank, around 100 gallons. Get a Hagen filter that hangs on the back, say an AC 50 and use some poly fiber padding filter media from Acurel. This filter isn't too strong and the poly fiber will attract and hold the small floating particles that make the water hazy.
Save the canister for a much larger tank. More filtration isn't better, it's just more. The key to clear water and a healthy tank is a good poly fiber filter media and large, weekly water changes. Work up to the point you're removing and replacing at least half the water weekly and service the filter regularly and you'll have few, if any tank problems.
"Fear not my child, just change the tank water."