Here's a pic of the shelves holding the 16 x 7 ltr tanks the tanks are 20cm cubes. Yes, there's one missing. It's in the bathroom. I took it there to wash it, got distracted and it's been sitting in the bathroom for a couple of weeks now.
These tanks hold my breeders. Unfiltered at the moment. There were sponge filters in all of them but I took the filters out to when I was doing a spring clean to give them a good wash, didn't get around to it, then my imported fish arrived and they had to go in there without filters. That was in November!!! LOL. But the males prefer still water anyway so even when the filters were in there before I used to remove the males filter when I was trying to spawn him. I use these small tanks as spawning tanks as well. I just put the female in the next tank, card and uncard, then just lift her out and pop her in next door.