cure the problem
First, can't leave the boat for days on end without clorinating your water. The boats are best used constantly. Treat the water in your tanks just like a swimming pool. Get a pool test kit and check for PH and Cl2. If cruising then use a water maker and the water will be sterile however it won't remain that way for ever. There is no perfect solution other than constantly using the boat or draing/refil the tanks every time you leave/return. If not cruising and don't want to spend bucks for water maker then add cap full of clorox to each tank upon departure (mix it in) and the water should keep a week. Learn somthing about water quality. Mitch Witt
