UNplug the HEATER if you have one. An aquarium heater will break if not in water! This is for your tank only, am assuming you have already netted your fish/ snails/ other creatures and put them into a suitable container. I use a 5 gallon bucket, it also holds my tank cleaning supplies when I am not using them. Leave your filter dirty, but unplug it, you will need the beneficial bacteria to recycle your tank. IF you had a disease problem, then you must clean your filter and use new...