So for 6 years I used a Rena Smartheater. I entirely made of thermoplastic and fits at the end of the intake tube of my Rena Filstar XP3, taking the place of the strainer normally there. For 6 years it worked flawlessly kept my 25 gallon tank at a rock steady 76 degrees. For some reason Rena discounted this heater a couple of years ago and almost as if on que mine started behaving erratically, one day I found my tank at 83 degreess and the heater was still on. Luckily, I caught it before it turned my tank into seafood gumbo.
PROs: Reliable, bombproof/turtleproof, integrates with Rena filters, accurate
CONs: Discontinued, large ugly cylon like light, temperature settings were hard to read, can be difficult to clean since it's a hollow tube
I've since replaced it with a 200w Hydor Inline heater. This heater does not go inside the aquarium but attaches to the output tubing of your canister filter. Comes in 5/8th inch and 1 inch ID models, most canister filters use 5/8 ID tubing. Installation took all of 10 minutes, I spend 5 minutes trying to find a spot on your output hose where I wanted to splice the heater. I think closer to the output the better, less chance of thermo heat loss. Cut the tube with a sharp pair of scissors, push tube onto the heater tube barbs making sure the arrow on the unit points in the direction of flow. Tighten the nuts and your basically done. No more ugly heater in the tank.
I've had it for over a month now, and it been working perfectly.
PROs: No tank space used, easy to read temp. dial, set and forget, has that Italian luxury mystique
CONs: Must have a canister filter, temp dial lacks a lock you have to be careful you don't accidentally knock it, instructions minimal
