Keep at least 2 of every size you guys carry.
Or go get a roll of media filter. Keep a section on your truck and cut it to the size you need when you need it. Makes a great emergency filter for HO and you don't have to carry a van load of filters.
I fully support the military and the War on Terrorism.
If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.
If you do know, then do. But do it right. Otherwise, you may not be doing it long.