Heater this and that

[Hobbiest]

I just set up a 90. I thought I was putting my best two heaters in it. A 250 watt Aqueon and a 200 watt Ehiem. But the temp was down to 73 and falling. Both kick on briefly. Finally I had to throw a 100 watt that I can't think of name for and the temp is rising now. The two big boys are set at 80. The Aqueon runs a little (red light) then standby (green). The Ehiems light comes on but not for long. Irritating with the temp at
73 and both heaters set for 80.

[mibwb]

Rule of thumb 5 watts per one gallon of water. You have the right amount..two heaters equaling 450 watts. Heaters should be placed one at each end of the aquarium. This way you are heating two sections of the aquarium and they will run better. It sounds like you have them too close together so they're hampering each other's operation or if they're set up at each end, then you've not given them enough time to heat the entire aquarium water volume....this includes substrate and what ever else is in the water column.

[Hobbiest]

Thank you. I was a digital thermometer malfunction.

[mibwb]

Thank you. I was a digital thermometer malfunction.

Then there's that too....was hoping something simple and not equipment malfunction.  Always have two different types of thermometers, just to be sure and safe.