Nature2 silver ion sanitzer is what I have in my Hot Springs spa. Also at some web sites I have read that with the silver ion and continous ozonizer that I don't need to use chlorine. All I need is to shock with MPS regularly. Could the experts weight in.

Well it lasted one week. For the 1st week after filling the tub I didn't add chlorine but kept the proper amount of residual MPS in the tub. I took a sample in for analysis and they were wondering where the chlorine was. The end they told me that the chlorine activated the silver ion cartridge. Now what a minute I thought the MPS would do that. So not wanting to make someone sick I added chlorine. So where do I find the final say on what does what for sanatation o a natuere2 system?

You don't need chlorine to "activate" the Silver Ion cartridges.

But you might like the water better with Chlorine over MPS. Have you tried sodium dichlor as your primary sanitizer?

You can still shock with MPS (it will take 3x as much MPS as it does chlorine, which will affect your PH)

Just try sodium dichlor type chlorine- add about 1 teaspoon after each use, or if it's been several days since you've been n the tub, add 1/2 teaspoon before you hop in.

You won't be able to detect it's presence-the levels are so low, it's impossible to smell. Also, unlike the MPS, it won't change your PH.

If the only benefit to a non-chlorine agent like MPS is higher cost, more work, and poorer sanitation, what's the big deal about being chlorine free? When used properly, sodium dichlor treated water is the most natural, chemical free smelling water possible.

In your case, I'd add an ozoneator. You'd see tremendous benefits, and could even use less chlorine.

My SPA does have an ozonator. Yea me thinks you may be right. I also have been using diclor but had some bad issues with combined chlorine. Will the MPS shock once a week control my combined chlorine?

Yes MPS will help reduce your combined chlorine if you're using a super-oxidation dose. A shock with chlorine will overcome combined chlorine as well. With both chemicals, you need to add an additional amount over and above the normal amount to shock/oxidize your 355 gallons.
Some additional info here http://www.scarritt.com/spasanitizing.htm

The directions for Nature 2 does say that you need to break in the stick with a higher level of sanitizer(chlorine) for a few days.