Is this one of the inflatable hot tubs? I had one before I got my Marquis and used it for 2 seasons by my pool. I was shocked at how well these things work for the money and it is what made me decide to get a full blown hot tub that I could use year round (I live in a colder climate where the lay z boy does not work in cooler seasons).
So are you using bromine as your sanitizer? Did you add a sodium bromide before shocking? And what type of chlorine did you use as the shock? If bromine, it sounds like you either didn't get enough sodium bromide in the water before shocking or didn't put any in there. I think you need to build up a bank of bromide in order for the shock to activate it. If you didn't, after 48 hours, the shock you added will most likely break down and will continue to fall to zero. If you did add bromide, then when you shocked it the readings should have gone up pretty quickly. What are your readings now?
I tried bromine but ended up going back to chlorine as it was easier to manage for me. Some dichlor powder every day keeps my water sanitized and at lower chemical levels for when I use it.
You also need to make sure you have you PH and Alkalinity in line or your sanitizer won't be as effective.
