chlorine levels won't stablize

[cohomojo]

First time I've been on this site, but am having problems with hot tub so I started checking things out and ended up here.
I was having problems maintaining Bromine levels so decided to go back to Chlorine.  Flushed and drained the hot tub like I've always done.
Refilled (500 gallons), added some stain and scale defense, 1 bottle of metal be gone, and then once the spa was filled started adding Calcium in 6 tablespoon increments until I had the proper readings...checked Ph and ALK and all was good.
Put 1 1/2 Tablespoons of Chlorine in spa and ran for 30 mins....Nothing on the test strips....in the last couple days I've probably added 3-4 tablespoons of chlorine.  I finally got a good reading yesterday morning, but by the evening I was reading nothing.
Haven't used Chlorine in a long time, but something just doesn't seem right.  Should I keeep adding chlorine or what.  Seems it doesn't even last a day.

[rin-spa-aic]

I had a high chlorine demand on my spa and eventually seemed to control it by adding borates.
If you have the venturi jets open it will also tend to use chlorine faster in my experience.


Are you testing the stabilizer too?

On my spa I use dichlor until the stabilizer hits at the bottom of acceptable range on a test strip.

Then I added borates (borax+muriatic acid) and switched to bleach.  Chlorine demand has been very stable since then.