My Softub requires the use of chlorine (not bromine) for maintaining the 5 year warranty (at least in the US, the Candanian warranty is different, I believe). The sanitizer they sell is Dichlor and they recommend replacing the water every 2 to 3 months because it becomes "unstable". Yeah, because the CYA levels go sky high!!

My 300gal Softub tested at over 100ppm CYA using the sight test after using DiChlor for about a month (one TBSP about 3 times a week). It was over 300 on the strips after 3 months of using DiChlor. Yikes!

Anyway, I too have decided to try BBB. I have found that about 1 to 1 1/2 oz of regular bleach will get the tub to 3 to 4 ppm and keep it above 2 for a day or so. The only problem I have found is that the PH seems to jump around more, but since I didn't start with "fresh" water (I had been using DiChlor for several weeks before testing then switching), I'm not going to worry until next fill. Then I will use Borax to hopefully buffer the PH better.

Anyway, so far the results have been good. Water is clear, no itch, no noticeable film on the vinyl. As Richard says, biofilms do get started in hot tubs and the only way to clear them is a pretty good shocking. I want to try this with a complete refresh of the water, but as of right now, my DiChlor is put away and I have a nice quart bottle of bleach and a measuring cup in my tub kit.