I use Nature 2, the yellow one.
We have a 8x8 5 person tub.

I'm supplementing with cholrine once a week and a shock every time we use the tub. My PH and other readings are fine but my chlorine level is always non-existant on the test strip. Should I not worry about this because of having the Nature 2? How do I know i'm getting enough chorine to supplement? I'm adding 1 1/2 T a week of chorine per the instructions I was given. The shock prior to using the tub is also 1 1/2 T.

I would be using chlorine daily - unless you have ozone on the spa. If you do have ozone that is why you get no reading on the chlorine - ozone eats it up. If you do have ozone you are doing it correctly. Shock before usage, chlorine weekly and replace tha nature 2 every 4 months.

Hope this helps,

Pete
HotSpring Tech