I currently have 2 tanks and both have the same issue. The 10 gallon has an aqueon 50w adjustable heater and the 29 gallon has a marine land 100w adjustable heater. Both of these tanks are staying only 2 or 3 degrees higher than the room temperature no matter what they are set on. Is this a case of undersized heaters or bad heaters? What are the best heaters to buy?