Since your using dichlor ...
My OPINION is I have to question the effectiveness of Nature 2 at being a sanitizer. It's not a primary sanitizer, it's a secondary. That means you really shouldn't rely on it sanitizing the tub - If you have a lot of people in it, it won't be able to handle the load.
But to answer your question somewhat. I use dichlor AFTER I get into the tub. I'm sure that you've heard about Vermonter and Northman. If not, go to rhtubs - go to the forum and look under the FAQ.
Basically you need to put enough dichlor into your tub to reach 2 to 3 PPM about 20 min after putting it in. It all depends on how many people use your tub at a specific time - if it's just you, maybe 1 teaspoon; but if you have 6 people in it maybe 2 tablespoons. I do have MPS and have used it twice in the 1 1/2 months that I've had the tub. My dealer gave me a dichlor shock product that has MPS in it I believe and I'm trying to use that up. The idea is use dichlor all the time and MPS to shock the tub once a week so dichlor can do it's job.
As for calcium hardness, I believe water should be "balanced". Balanced water is water that has all it's parameters in a specific range, calcium is one of them. Go to a spa or pool store and ask them for calcium increaser - I believe it's calcium chloride. To test, I use a Taylor kit, but I think some test strips test for it also. you want the calcium hardness to be about 200 PPM - If it's below a certain point (150 ?) it can cause excessive foaming as per the experts here.
I would adjust PH first to 7.2 to 7.5, alkalinity may or may not fall into the proper range - it helps the PH stay stable. then adjust calcium (if you know the volume of your tub, a store may be able to tell you put in [this much] calcium increaser), put in some chlorine to get some sanitizer in the tub and enjoy the tub.
After you get out - put enough chlorine in the tub for the 2 - 3 PPM and IF you don't go in for about 12 hours (overnight or morning/evening) you'll be soaking in minimal chlorine. Once a week shock with the MPS (you should substitute dichlor once in a while - super chlorination kills almost everything nasty in the tub), clean or change the filters (this is an important step) and your good to go. ALSO!!! - IF you have a lot of people in your tub - clean the filters the next day - I've learned this the hard way TWICE - spa filtration is different from pool filtration (if you own a pool).
I hope this helps and if you have any questions, please ask!
