A killie comparison from long ago might leave them similar in size to
gardneri. (Not that their mouths are similar in size though.) Once on a
visit to Ed Warmer (a gentleman who made a living breeding and raising
killies) , I was surprised to see a pair of Celebes rainbows (the only
non-killies in the place) in his standard killie egg production tank (2 1/2
gallon tank, sponge filter, close fitting top, mop...). That seemed too
small for a rainbow, but it worked for him with frequent water changes. Egg
grow out was in larger containers and tanks, starting with plastic dish
washing trays dedicated to the newborn fry. He seemed to do ok with freshly
hatched SF Bay newly hatched baby bs.
It is too pretty and active a fish to normally keep in such a small tank.
All the best!
Scott
Who lives where it will soon be too cold for Peter's damnbusia to
over-winter.