Welcome.. you are close to my hometown I grew up in long ago :)
What food are you feeding?
How much of it?
How often are you feeding?
How big is the tank?
Depending upon size of the tank, filter, live plants, cycling it varies on how much and often it needs changing. It will always need a weekly change, but the smaller they are, and with no filter, the more they need it.
When feeding, it's always good to be careful not to put too much food in there.. and using a net or turkey baster, remove any uneaten food within minutes of feeding to avoid it fouling up the tank.