SLAM Question (to reduce CC)

[slothanarchy]

We currently have an above ground, 500 gal hot tub with ozonator. It's only 4 months old. When we first got it, we did the Ahsome flush. The last new/clean fill we did was about a month ago, and things were going really well. We use 10% sodium hypochlorite to sanitize. CC was consistently at .5 or below. With this last fill, I tested the overnight demand and there was a 60% loss. I think, due to the ozonator, this hot tub has a high chlorine demand.

My husband and some friends hung out in the hot tub last weekend for hours and didn't replenish any of the chlorine. The next day, I tested and FC was 0, CC was 1. The water was also very cloudy. so I thought I would try to SLAM. I've been doing it for 3 days now keeping it at 13ppm (as best as I can). The water has cleared up and is no longer cloudy. Initially, I was losing 5ppm chlorine every hour. Now, it's about 1-2ppm every 3 hours. Unfortunately the CC is still somewhere between .5 and 1ppm (I'm using the Taylor K-2006 kit, at the 10ml level). 

Am I understanding this correctly, I keep chlorine levels up until CC drops below .5ppm? Thanks!

pH = 7.4
CYA = 30
Temp = 96%F
 

[MPurcell]

Yes, your understanding is essentially correct. SLAM instructions at Trouble Free Pool forum are for pools, but the principle should be the same for a hot tub. The hard part is the OCLT, since the high temperature tends to make the chlorine dissipate more quickly. If the tub is completely free of contaminates and has been held at shock level for over 24 hours that way, the combined chlorine should really be zero.

[slothanarchy]

I work from home so I'm able to maintain the shock level during the day but how do you keep it up overnight? Should I be raising it higher than the shock level before going to bed so that it never falls below the shock level during the night? I tried this the first night, but the other 3 nights I didn't. 

Edit: at 8pm last night, FC was 13, CC was 1
at 8am this morning (12 hours), FC is 6, CC is 1

[MPurcell]

With that level of loss, slightly more than 50%, you still have something in the tub eating up chlorine. I assume you have cartridge filters. Pull and clean the filters completely, and then put them back in. I bet they are very dirty, and may be contributing to the chlorine loss. Remember that SLAM protocol for a pool is mainly to deal with algae, which is not the problem you are dealing with. Just let the chlorine come down overnight and bring it back up the next morning will be fine.

Was the tub new or used when you got it four months ago? Did you do another ahh-some flush one month ago when you refilled? I'm wondering if there is still a bit of biofilm in the plumbing as well.

As a point of reference, I just refilled my small (230 gal) tub last weekend. My initial 24 hour chlorine loss was 20%, from 20 ppm to 16 ppm on the second day after fill, with the tub heated and the lid on. Yesterday for 24 hours I had the temp down to 80 degrees and the tub lid off, and the 24 hour chlorine use was only 1 ppm, from 10 ppm to 9 ppm. I put too much chlorine in when I filled it, and have been waiting for it to come down before we use it. The CC has been 0 all week.

[dlleno]

ozone does eat chlorine, so its hard to translate the various rules of thumb (for chlorine decay)  into something meaningful for hot tubs with ozone.  my inclination is that 50% decay rate you've got biofilms.  Purge with ahh-some (including the filters) more than once until you achieve an ahh-some dosed spa, with filters installed in their normal positions, and you get no new release of material.  thats the measure of success --   sometimes it takes only two drains to achieve this,  and sometimes many more. the point is you really don't know if your spa is clean with only one purge -- you have to prove that your spa is clean by dosing again  (and sometimes again) with ahh-some.  you will soon learn what an effective purge routine is for you, and you will get to the point where you don't have to do the "squeaky clean" test all the time.   

Once you achieve the "squeaky clean spa" then you can establish the chlorine decay rate that is accurate for your spa.