I'm no good changing gallons into feet

For my 3ft tank I use a Fluval U3 inside it + have bought another so I can use them in the new 4ft tanks. I don't know how much heat they produce, as I've always had it in the 3ft tank + not tried without. I did discover that the water flow was too much with it standing vertically, but it fits it PERFECTLY along 1 side (1ft) lying down horizontally + with the minimum flow, plus the output directed at the side of the tank, they seem very happy with it.
For my 2ft tank (STILL temporarily housing my adult male), I have a sponge filter, powered by a Tetratec 10-60l APS50 air pump (which has a flow control value, allowing me to avoid strong water movement), with the filter's output pointing into a corner of the tank.
For my friend's 2.5ft tank, I again have a sponge filter. This 1 is powered by a Marina Cool O2 air pump for up to 20l / 4.5gal. I don't think it is anywhere near powerful enough to be permanent, but I needed the cheapest I could find because the axies in this tank were being kept in isolation for recovery purposes + under my care 1 of them grew from 12cm to 16.5cm in just 1 month + was in desperate need of being in a more axie-friendly environment. The filter output is again pointed at the corner of the tank + despite not having a variable flow valve, it isn't too strong. I do need to do more regular water changes with this tank though, since the filter isn't strong enough. It was more to keep the water aerated + avoid 100% water changes in the tubs every evening!
I'd definately advise the sponge filters for younger axies, but that's just personal preference
