Yep, Seachem makes a 25 watt fully adjustable heater that is fully submersible as well. The small pads or tube type heaters of 7.5 watts that are non adjustable will work, but yu have to be very carefull as they are desigined to keep the tank 3 to 5 deg above ambient temp, so if the tank heats to say 80 deg with lights on it, then that tank can in theory get to 85 deg with that heater trying to keep it 3 to 5 deg higher than ambient which in all reality is the actual water temp its referenceing. I think if I remember correctly that the hydor brand does have a temp limit of 92 deg or so, MAX temp...but by then its all over but the crying anyhow. I use the 25 watt adjust seachems in my picos and have yet to have a problem.
