My new 2.5 gallon fish tank with a divider arrived today. I also bought a filter and a heater (Hagen Elite Underwater Mini Filter, UL Listed+ Elite Submersible Preset Heater Mini, 25-Watt.)
The fillter doesn't seem to work out in a tank with a divider; one fish seemed struggling to swim anywhere and was being sucked toward it. So I turned it off. He now just hides behind it.
The other one LOVES the heater and sits next to it. However the water on his side is noticeably warmer than the other side. I suspect this has to do with the divider. I can't add water to the top (allowing water exchange) because the fish must be kept apart.
First, will this always be? Will one part of the tank be colder than the other? Second, will this bake my fish, as it is only heating one side of the tank? I don't see an option to set a temperature, either.
Here's a photo: