You have been so very helpful! Thanks so much! I have one further question/dilemma. I got some medicine (unfortunately couldn't get hold of the one you suggested) and it requires me to remove the carbon from my filter. My filter has the carbon impregnated black sponge. I assume I must remove this as per instructions, but my question is, do I need to put anything in there as a temporary replacement, or run the filter minus the sponge? Also, how will I keep the bacteria alive on the sponge if I have to remove it for several days? Won't this completely undo all the good work we've just done!? If you can help me with this I'd be eternally grateful!