I have a short, colourless, slimy sort of coating on everything in the tank just about, especially my gravel. I would appreciate any help. My first thoughts are maybe rotting food and what not so I have bought three new Cory's and six zebra snails to try and help if that's the case. I just wanted to post in case any one had any other ideas or solutions. It's a 29g tank I have had set up for three years. Right now it is only guppies and the previous mentioned fish. I have tried to upload pictures but I'm Not sure how clear they will be or if they will even work.