Shock the pool with bleach and keep it at shock level until your FC away from the return is holding. Your pool has a chlorine demand from the algae and because of the size of it you are near the limit of what the cell can produce (the turbo cell 15 is rated for 40k residential or 25k commercial). Once you get the algae taken care of I think your SWG will work fine. You probably have another year or two left in the cell if you have taken care of it.