OK guys, here's hoping for some good advice....
I've tested the water and the readings are: pH 7.8, Amonia 0ppm, Nitrite 0ppm and Nitrate 20-40ppm
The tank is a 30 litre BioOrb and I am down to one molly and one ghost catfish, they seem quite happy now, the water is clear and the sponge in the...