I have two 150 watt Aqueon submersible heaters neither can be set to deliver accurate temperatures . I use one in a 37 gallon tank and I have it turned up all the way and it won't raise the temperature in the tank above 85 degrees! Ordinarily this would not be a problem, however I am treating the tank for Ich and would like to get the temperature up to 87 degrees. Should I be using a 200 watt heater? Or are there better brands out there?