I was thinking maybe some lemons and cardinals.. How many will fit in my tank? I don't want to over croud them.. Will 25 tetras, 10 Cory catfish and 2 SDs fit in 250ltrs?
Ok now that I know what you're routine is go for it with a total of 25 tetra's total , but if any changes in the parameters remove some of the fish. Cardinal tetra are sensitive to ph change so acclimate them very carefully.