So I'm getting a 20g from an old fish breeder who is getting outa the business. she is going to leave the tank part full of water from the old fish that were in it so it will be ready to go for fish after a couple days. but i won't be able to get the fish for the tank till January and I'm picking the tank up tomorrow. will this be a problem or if i keep the filters running will it be fine till Jan? or should i get a couple like snails to throw into it till then? all help is appreciated.