Recently, I've been noticing my water getting a bit too warm, so I went out and got a thermometer for the tank. it seems to be near 90 degrees, so I tried adjusting the heater, but I've found out that it doesn't really work no matter how far down I turn the knob, the thing seems to always go full blast. I don't know if I should turn it off or anything, as my tank has guppies and corydoras, and they seem to be a bit uncomfortable but not sick or too stressed. I don't have the most money to spend on the hobby, but if you guys have any suggestions or solutions to fixing the heater, they would be appreciated. Otherwise, I will get a new, working heater.