Is your hot tub water cloudy and you've tried everything to clear it up? You've balanced your chemicals, you've shocked the water, you've cleaned your filter, and it's still merky. Well, chances are that there's Gunk built up inside your hot tub pipes, and this buildup over time forms a layer of bofilm that's resistant to normal chemicals and biofilm inside your plumbing causes cloudy water, smelly odors, scum lines, and slime. No matter how balanced your water is, you need to purge your pipes to get rid of it. So use a hot tub line, flush and change out your hot tub water every 3 to four months to remove bofilm buildup.