I currently have a Royal Gramma, Pygmy Cherub Angel, Yellow Watchman Goby and a mated pair of Boxer Shrimps. My tank is a 90 litre tank and I'm about to add a TMC v2 400 skimmer (rated for a 400litre tank, although I have had extend pipe work to mod it to my tank which will take performance down a touch). Is it possible to add another fish? I'm looking at adding a purple firefish