Get a larger filter if it isn't large enough already and do 25% water changes.
No need to do 50% every time, I never have and I have fish 7+ years that are still alive, my first fish actually.
Good filtration is the key to good quality water.
Many people hype everyone up on how they need all this crap for the tanks and 50% water changes every week and all that.
Watch your tank and do what you think you need to do for routine maintenance.
I've gone almost 2 month without a water change and no sick fish, no water problems of any kind. My tank also wasn't messy, small fish, small mess and good filtration.
Just my opinion.