Marks,
I too use the Nature2 and dichlor along with an ozonator and have had great luck with water quality.
My suggestion would be to take a sample of your water out of the tap to your dealer and let them run a free test on it, so you will know what you are working with from the get go in the future.
As for now, your TA isn't bad at 100...I've heard a range of 80 to 120 is good. Ph is more important though. 7.2 is a little low but nothign to be alarmed about. The key is taking your time adding chemicals. Always add a little less (you can add more but you can't take out!) and then wait a day before you check again.
I used to want to add chemicals, then run the jets and check the readings again in 30 minutes but that's not always a good idea. Give things time to settle down and then if it needs additional treatment, do it again tomorrow. A day or two of a low or high reading of one thing or another is not going to destroy your tub.
Also, handle one problem at a time, don't try to fix Ph, TA and Calcium Hardness all at one time. One thing usually affects another so its best to get one item fixed and move on to the next. Good luck with everything, I think you'll be fine!
-Sarge
