I have a 2008 Sundance Cameo (450 gal) spa with ozone. To date I've been using Sundance's Nature2 equivalent (MPS + mineral cartridges) with mostly positive results. But after stumbling across the dichlor-then-bleach method, I decided to give it a try.
Today I drained the spa, flushed with Sea Klear system flush, filled it from my well through a "prefresh" filter (as always) and then balanced the water per the recipe (my TA is ~60ppm, PH is ~7.8, and CH is ~130). I also added about 1.5 cups of ProTeam's Gentle Spa to yield ~50 ppm borates.
After balancing the water, it looked sparkling clean. Then I shocked using dichlor to about 10ppm (~1oz dry weight dichlor). The water turned green immediately, not a cloudy green, but more translucent. This has never happened to me before, but to be honest I never added more than a tablespoon or so of dichlor at one time for the weekly shock (i.e., MPS was used for daily oxidation).
I suspect the cause is metal in my well water (likely copper?) but before I add a metal sequestering agent (like Leisure Time's Metal Gone) I thought I'd seek other opinions from knowledgeable folks on this forum. My preference is to add as few chemicals as possible to evaluate how well dichlor-then-bleach works alone, but if I need to add a metal remover to prevent spa shell staining, I certainly will!