Hi Everyone! And thanks for sharing so much great information! I've been reading this forum for some time I bought a brand new Sundance spa (325 gal) with Nature 2 system last June. I started getting a rash in August last summer. Have been working with the spa dealer and have changed from chlorine to bromine and now back to chlorine with the MPS & Nature 2. I love my spa and qualify as a high user (1 hour or more each night). It's usually just me but occasionally one of my small dogs jumps in (not realizing the cover is off).
So initially I followed the dealer's instruction which is basically what I've read here Nature 2 + MPS followed by weekly chlorine shock with dichlor. When I got the first rash, I did some internet research & found this forum which is where I've found the best information most consistently. Anyway. I started using more chlorine which didn't seem to help the rash. I went to the doctor but she wasn't concerned -- didn't do any kind of test.
Then at one point the rash got much worse. so I changed from chlorine to bromine thinking that even though I've swam in chlorinated pools all my life with no issue maybe it was the chlorine. The rash after using the bromine was even worse. So I stayed out of the spa for a while dealer suggested just using the MPS and no chlorine or bromine. This didn't work because I would get foaming rather quickly.
After all these changes, I've noticed that the rash gets better and is fine when I add new water to the spa. Everything is fine until the foaming begins (about 2 weeks after water change). My last water change was March 7. So last night I decided to add whatever it took to kill the foam add calcium ... super chlorinate borax
I added the calcium yesterday (CH was very low; now over 100). I superchlorinated last night. Today the FC was low (not zero, but low). The water was perfectly clear but I noticed that the pH was dropping. So I added borax (had never added any ever before) just 1 cup (about half of what the Pool Calculator said to add). The water got super cloudy. But the foaming is totally gone. The pH was high so I added dry acid. Now the pH seems fine but the water is still quite cloudy.
I will be changing out the water next week, because I will be moving the spa to its new patio.