04-23-2008, 01:57 PM
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Watch the light on the heater, does it go on and off to indicate its kicking in?
What kind of circulation is in the tank? If there is heavy circulation, that will cool the water temp and even a powerful heater won't be able to keep up with it. A good example for you is my 120 quarantine tank for my oscar... Because of the medical issue, circulation had to be greatly increased in the tank... in 120 gallons I had a 200 watt heater, which is normally plenty for that size of a tank. I was having a difficult time keeping the temp above 74 this way, and it required me to add another 200 watt heater to bring the temp up to 80 where it needed to be. Once we decreased the circulation, one of the heaters had to be unplugged because the temp went up to 84 within a few hours.
Also, watch where the heaters are located... are they in the way of water coming back into the tank from the filter(s)? Are they near an air stone? All of these things can greatly affect a perfectly fine heater.
If there are still worries about whether they work, set each one at 80, and one at a time put them into a small tank that should have no problem reaching 80 degrees with that size of a heater... and watch... do they turn on and off properly when the temp reaches 80? Run the smaller tank with no filter, so you get a better feel for how well the heaters may or may not be working. It could very well be you have a faulty heater...
If you find you need to replace 1 or both heaters, try working with the Aqueon subermsible heaters... they're inexpensive and work about the best of all on the market.
One last note... when testing the heaters in another container... unplug them one at a time, as you're going to test them, and let them sit in the main tank unplugged for at least 15 minutes before moving them out to the test tank. Once in the test tank, again let it sit for 15 minutes before plugging it in. A drastic change in water temp on a hot or cold heater will cause the casing to crack, which can be a huge fire hazard and can cause electrical shock to you and/or your fish if you make contact with the water.