New to water chemistry / Non Chlorine shock?

[angromarsi]

Hi! I am a new owner of a Sundance Hamilton spa, which we have had for about 3 weeks now.  I tried following the directions of my dealer and the materials he gave me, but not sure it was the best advice.  They've offered to test the water, but we live an hour away and it's really inconvenient.  I've done a lot of reading of old posts on here and bought a Taylor water chemistry test kit K-2006.  I've pretty much gotten the hang of testing and realized that we have been adding WAY too much di-chlor which increased my stabilizer/CYA levels tremendously in only 2 weeks time!! 

Since we're in a cold climate we were hesitant to fully drain the spa, but last night, my husband drained down to the bench level and refilled new so we could get some of the CYA levels out. 

I've been using the wheel and tables that came with the test kit and for the most part have been able to balance the water, but I'm still really confused about when Non chlorine shock is supposed to be used and how you know when to use it and how much. 

This morning, after the refill, I added 3 oz of metal out (we've not had our city tap water tested for metals but the dealer recommended we add some to be on the safe side...)  Temp is back up to 102.  My levels were:
pH: 7.6
TA: 90 ppm
CH: 120 ppm
FC: .2 ppm
CC: .2 ppm
CYA: still measuring high around 55 ppm

I believe we have just under 400 gallons in the spa.  It's new, so the two of us use it about 5 times a week for 20-60 minutes at a time.  2 Kids (4 &6) are in with us about 2 times a week.  I went ahead and added .5 oz of dichlor, which I was hoping would bring my FC level up 3 ppm.  So--I'm still not sure I understand the non chlorine shock.  Can anyone help to explain?  Thanks!

[ericelyse]

One thing you can use to instead of di-chlor to get rid of CYA  is lithium. We used it for a few month (before realizing my husband was allergic to chlorine) but lithium was so far my favorite method.  I used it to shock the water too.  One thing i like about lithium is that it dissipate quick and you add it after you bathe. No build up of CYA in the water. No MPSneeded.   Water was super clear.  Chlorine works at his 100% power. When there is CYA in the water, it slows down the sanitizing process and oxidizing power.

[ericelyse]

And we also had a 400 gallons spa too.  1/4 cup of lithium would bring the chlorine to 10ppm.  So we were between 1/8 cup (5ppm) and 1/16cup per day, depending of how many persons would use it.  At 3ppm, the next morning it would be down to almost 0ppm, would bath in it and then add 1/16cup after I get out.  I would shock it when there was a difference between the free and the available chlorine, usually after when we had friends over and we were 4-6 in the tub.  Hope that help!

[chem geek]

The lithium hypochlorite is the only solid form of chlorine you can use that won't add other things you may not want or need such as Cyanuric Acid (CYA) from Dichlor or Calcium Hardness (CH) from Cal-Hypo.  It is, however, quite expensive.  You could also use unscented plain (not splash-less or outdoor) bleach but have to be careful not to spill it on clothes or other fabrics (it's bleach, after all).

Just remember that you want SOME CYA in the water since having none at all would have the chlorine be far too strong.  A CYA of 30 ppm or so should be fine.

Many people use Dichlor-only and while it's true that the CYA builds up they just change the water more frequently.  With the Dichlor-then-bleach method (or Dichlor-then-lithium hypochlorite if you prefer) you should be able to go at least twice as long between water changes.  You may need to add some more Dichlor once a month to make up for the CYA that slowly gets oxidized by chlorine at the rate of around 5 ppm CYA per month.