Originally Posted by Byron
On heaters, don't try to "save money." No single piece of equipment in an aquarium is as important as the heater; a malfunction either way (no heat or over heat) can kill fish overnight.
Buy the best you can afford, and the higher wattage. Higher wattage heaters have to work less to do the job so they last longer and are less likely to malfunction. I don't see the tank size mentioned, but having two is another way to preserve the heater as two work less time than one. In anything under a 3-foot tank, say 30-40 gallons, one 150w or 200w heater works best. In larger tanks, two 150w or 200w (or higher if very large tank) are better, one at either end and preferably next to the filter outflow and intake.
I have a 150w in my 10g and it works like a charm. My 20g has a 200w as does my 33g. I have had 3 or 4 50w heaters fail in these tanks, but never the higher wattage and they keep the water temp much more stable.
Heaters are a total PITA. Lower wattages get worked harder. High wattages will cook your tank faster if the get get stuck on. Had a 300 watt theo hydor on my 55gallon, first heat malfunction I had. Got stuck on and was no fun. Replaced with a Rena smart heater which stopped working under warranty, replacement stopped working again about a year after I got it. I currently have a 200 or 300 watt heater in that tank, I forget which wattage. The current one is a sera which seems to be working quite well and was on the cheap side, I needed something with a guard. The Rena it replaced came back to life and I intend to put it back into service eventually. I left it in a bag o rice for over a month.
I couldn't tell you the wattages or even brands of half of my heaters. The one in my 20 gallon has been going strong and so far is my longest lived heater. I has a lot of condensation, and water droplets inside of it. I just spent 10 minuets trying to set my heater for my fry tank. Its the heater I hate the most. Extremely difficult to set temp on it. Then I have a really cheap non submersible clip on side heater that is always reliable and is my 2nd oldest heater. I quite like these. I can actually take them apart are fix them if something does go wrong. I once submerged mine and had to fix it.
Heaters are entirely hit and miss IMO. I've bought some expensive ones that simply don't hold up. Have some cheap ones that don't give up. Really hit an miss. My local fish forum has a really interesting thread going now. Seems some badddddddddd shipments of the new Marineland stealth heater pro came into our area. I understand no heat/over heat, but these things are legitimately exploding depth charge style. Shattering large(55g) tanks killing fish and heater totally blown to bits. Marineland is a well know brand too and these are suppose to be reliable heaters, but from what I have seen these new ones are NOT something you want to play with. Chances are they will work just fine, but there is a small chance it could physically destroy your tank. This is not a random incident either Marineland is accepting certain lot numbers back for refunds/replacements no questions asked.