OK, I've been reading a LOT of info on this forum as well as doing other research and I'm confused about the ability to cycle a tank under 5 gallons.
From what I understand, the ability of a tank to hold a stable cycle is directly dependent upon the amount of surface area in that tank on things like the substrate, decor and the filter. And from what I understand, the vast majority of the BB colonize in the filter.
So... A smaller tank may have less general surface area in the way of tank walls, substrate and decor, but if it has something like a sponge filter in it, and those are known for the amount of surface area they contain for the growth of BB, then wouldn't they be able to allow a smaller tank to establish and hold a stable cycle?
I honestly want to know 'cause I've been pondering this question for weeks.
I've got mostly 5 gallon tanks myself, and I prefer cycled tanks, but I'm running out of room and a 3-4 gallon tank might fit better in some places but I don't want to have to deal with multiple water changes each week.