G'day all, I've bought a 4 footer to give the discus in my 3 footer some more room to move. I currently have 4 discus, 5 Sterbais, 9 Rummynose in my tank. What i want to know is how many tetras can I add when i go up to a four. I would like an even number of Rummynose and Cardinals.

How does 20/20 sound? Or can i safely go higher?