How much FC should I lose each day / overnight

ryadre

Active member
Sep 8, 2019
34
New Zealand
We have been running this tub for nearly the last 2 weeks, fresh filled using filtered town water
From there I followed the recommended chlorine guideline post.
Added dichlor to get the CYA up to 30ppm (had to add a bit more than calculated dose)
Using 13% liquid pool chlorine - although I wonder if it isnt as strong as that as It doesnt quite calculate using pool math app.
Added boric acid 50ppm (about 350grams)
Added calcium to 125ppm
Added baking soda to TA is around 50-60
pH around 7.2 to 7.4

After the first week of all 5 (3 kids) of us using, the CC was up to 1ppm
This past weekend I upped the chlorine to over slam levels for 2 or 3 days
The CC is now down to 0.5, but it seems to lose maybe 3ppm overnight. Originally when I was upping the FC to around 14 it was dropping 6 or 6ppm
The pool is in a shady tree area so gets no sun, and I dont like leaving the cover off too long due to all the leaves and seeds that fall in.

Im currently learning how much bleach to put in after we get out at night, so there is enough for the next night before we get in. I think it is going to be maybe 100ml of this 13% bleach.
Adding 40ml of bleach seems to raise it by 2ppm - but Poolmath says it should raise by 4.2pppm.
I have a pretty accurate volume of water - I used a water meter when draining which gave me a reading of I think 1160 litres, plus what was left in the pool so am working on 1200 litres.

Another question I just thought of is, as there are 5 of us using the spa together it is easy to drop the FC while using it. If we had 4ppm FC it would get to 0 pretty quick, is that OK to have it at 0 for an hour, or should we start with FC up around 8 so hopefully there is a little FC left by the time we get out?

Anyone have any suggestions on anything I should change to my current schedule?
 
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I don't have any experience with a hot tub. I would be concerned about the shelf life of your 13% bleach. It will degrade quickly. Since your bleach may already be degraded, this may be the reason that you are not getting the expected FC change. Bleach that's about 5% will last a long time without degrading much. You might buy weaker bleach next time. If you are loosing 3ppm overnight after you get out of the hot tub, I'd slam again. I have heard of commercial pools using 8ppm of FC per day with a heavy bather load. This could be the case with your hot tub as well. I would never let my FC go below the minimum for my CYA. Be sure no one urinates in the hot tub. That could use up bleach fast and give the hot tub "that chlorine smell" from chloramines.
 
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