Nateness01

From what I've seen, it seems to come usually from someone wearing a suit or something that has residual soap or phosphates in it. Ours had the same problem after my daughter had a few friends over, the next morning it was solid foam to the lid. Never wash a swimsuit in laundry soap (there's no reason to.) Just rinse and hang dry, I prefer wearing swim briefs because they dry ten times faster than long shorts. Hope this helps.