I have had my 54L tank for just over 2 months now. I have a black mollie and 4 red serpaes, one died yesterday with swimmers bladder I am guessing.

My tank is well planted with live plants that grow very quickly, I have no idea what they are, but I cut the tops and replant.

The black mollie had Ich which is all cleared up and one of the tetras is a quiet fish that sits at the bottom in front of the filter, he eats and swims occassionally. My tetras don't school much, but I heard if they don't school they are very relaxed.

I would like to know should I be getting some catfish first to clean the bottom or what lovely colourful fish could I get next and how many. I am thinking maybe adding two more red serpaes as well.

Tetra are a schooling fish so they would probably be out and about more and hang in a group if you up the numbers to about 6-8.

There is no 'should' about what fish you need next, not everyone has or wants a clean up crew - maybe you could post some ideas about fish you would like to keep and we will let you whether we think they will all get along or not.

PS am moving this to freshwater as I think you will get more answers in there......