If you want all the tanks at the same temperature, then adding a circulating fan into the fishroom that keeps the air temperature stable from floor to ceiling helps with that. It "feels" counterproductive, to me at least, because it makes me much more comfortable in the room by giving the illusion of cooling, but it definitely mixes the air and helps eliminate stratification.
I recently installed a smallish on-demand heater specifically for the fish room, so that I have essentially limitless water at the correct temperature, and it is more efficient than drawing all that warm water from my old-fashioned whole-house tank-style water heater...so much so that I will be changing that over to a larger on-demand type for all my domestic hot water. When I say "I installed..." I am embarrassed to admit that I had to call upon the services of a plumber friend; the perfect combination of on-demand heater size and mixing valve turned out to be beyond my reptilian brain. Mixing valves are a dime a dozen if you want water for washing or bathing or other typical uses, and have city water pressure behind your faucets. However, getting a small unit set up to provide 75F water...especially when you are on a well and are utilizing a pressure tank for your water distribution, which operates on a relatively low pressure which is constantly fluctuating up and down during delivery...turned out to be quite the trick. If you are on a well, then expect some challenges if you go this route.
Finally...set up your air pump(s) to draw the warmest air possible. For me, that meant an air intake on the wall close to my upstairs wood stove. We get a significant percentage of our heating from a woodstove, and when it is operating the air in its vicinity is very warm. Building an extension onto the air intake from my central air pump, and running a dryer vent hose up to the intake near the stove, works well to stabilize my tank temps; the colder the weather is, the more the stove is used, and thus the more supplemental heat is added to the tanks which in turn reduces or eliminates the workload on the tank heaters.
The downside is that as I move more and more towards cool water tanks, I actually run the (warm) air from the pump manifold through long lengths of air line tubing held against the cold concrete, to re-cool it so that it doesn't heat the wrong tanks.