I bought a 500 Watt Titanium heater for the 100 gal RubberMaid Ag fish tank, thinking that was large enough since they are typically rated at 100-160 gallons.  At the maximum setting I am getting only about 72F out of it. Since I need to raise the temperature for the tilapia closer to 80+F, I am looking for 800W or 1000W unit, which will be the main heater. The current 500 W will be the back up.…