Ozone vs Vision vs Chlorine vs Dichlor vs MPS


Well-known member
May 13, 2008
I'm a little confused about the chemistry in my D1 spa. The manual talks about the ozone being the primary sanitizer. Then says you must choose a residual/secondary method: Vision (Ag ion) cart, Bromine, or Chlorine. I've been using vision.

With the vision method it says that acceptable Chlorine level 0-.5 (another place it says 0-1 as necessary).

1) can someone briefly explaing why that level is so low? Will having it higher adversely affect the ozone or ion actions?

The vision manual talks about testing MPS levels and adding MPS before/after each use.... doesn't seem very trouble free to me.

2) Big question what does the MPS do? Is it needed to make the ag ion work effectively or something? It also says you may substitute dichlor for these per use treatments. Which is preferred? I got a little spooked about using dichlor after reading about the effect of raising CYA... it was 75 before I replaced some water.

3) Should I be worried about high CYA levels since FC is not my primary sanitization method?

And then on to shocking. Yea the manual says "Never use Calcium Hypochloite." The manual talks about shocking w/ Dichlor to 10X CC. Or as an alternative w/ MPS.

4) What's the best method to shock my spa? Again, do I need to wory about CYA buildup? Should I keep my money and shock w/ bleach? What's the down side to "Never use Calcium Hypochlorite?"

I've always thought they kind of got me w/ always buying 2 bottles of stuff: the dichlor and the MPS. Seems I should be abble to get by w/ one or the other. Actually the last time I bought a bottle of "Enhanced Shock" it was actually 50% dichlor and "other"... which I'm assuming is MPS.

5) Lastly... I've seen it on here in a few places, I can't see why in the world droping a 1/2 oz or less of muriatic acid in the center of the spa could adversely affect anything. Of course spa store people always say NEVER! Thank you so much for the info here about lowering PH. I've always added a bit of dry acid for, churned the pumps on high to mix it up real good, and then cursing when checking it later only to see PH go up! Now I know about the outgassing process and PH rise w/ aeration.

Any thoughts and/or recommendations greatly appreciated...



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Platinum Supporter
TFP Expert
May 7, 2007
Silver Spring, MD
Ozone and chlorine tend to wipe each other out. Ozone and bromine are a much better combination, since ozone tends to reactivate bromine.

Vision appears to be a silver based system. Silver is a sanitizer, but not an oxidizer. Chlorine and bromine are both sanitizers and oxidizers. Ozone and MPS are oxidizers. You need both a sanitizer and an oxidizer. Silver is not a particularly good sanitizer, which is why they are telling you to add some chlorine along with the silver.

If you are using chlorine at all you need to worry about CYA levels. With fairly low chlorine usage and regular water replacement you might not need to worry about CYA levels very much.

Muriatic acid is only going to be a problem if you spill it directly on the spa walls. It mixes quickly with water as long as there is at least a little water movement (pump on).

I can't think of any reason they would say not to use cal-hypo. It adds calcium, but not all that quickly, and you usually are adding calcium to a spa anyway.

Bromine is probably the simplest system to use once you have gotten familiar with it. There are a few more steps than with chlorine, but you don't need to do them as often and fewer things tend to go wrong so it ends up being less work.