Chlorine drop with opaque covered pool: What's 'normal' for 24+ hours

[TimTucker]

I have recently drained and refilled my pool to lower the CYA (and I'm sure the TDS). The last fill was Saturday with 8.25% bleach added at sometime during the fill. NO MORE CHLORINE WAS ADDED. The next afternoon (Sunday 1pm) we took FAS/DPD chlorine readings:
FC: 7
CC: 0
the next evening (6pm)
FC: 5
cc: .5
today I have:
FC: 2.5
CC: 1.0

the other numbers from Sunday's testing:
TA:140
CH:225
CYA: 45 ppm

Is this a 'normal' drop rate? I saw the overnight drop rate limit of 1ppm. Would a full day be 3ppm? Any comments are appreciated. I've never had the ability to monitor this so closely, so please tolerate my ignorance here. I love this kit..., especially the stirrer plate.
I just SLAMed to 20 ppm using PoolMath of course.
Thanks,
Tim

 

[pooladdict]

Yes, your Chlorine numbers are very normal.

That TA is very high, have you also checked your Ph.? High Ph. and Calcium can cause scaling issues.

 

[TimTucker]

Thanks for the feedback! Sorry about the pH numbers. It was 7.6. Just checked it and found 8.2 or higher? I added 41 oz of 31.45% acid hoping the pH is 8.2. Will recheck tomorrow. My TA started out at 260 before the dump/fills.
Tim

 

[jblizzle]

Your minimum allowed FC level for your CYA level is 4ppm. Why didn't you add chlorine when you had the FC of 5ppm reading? You let the FC get too low. Although I guess you have now started the SLAM process.

If is "normal" in the summer to lose 2-4ppm of FC everyday (at normal FC levels). With a cover and as the water cools and the sun is less intense, the loss rate will drop.

 

[pwrstrk]

Treat your CYA level as though it was 50 and your FC target should be 8 and never below 4. ?

 

[TimTucker]

Why didn't you add chlorine when you had the FC of 5ppm reading?

Inexperience mainly. I see from the chart that 4 is the minimum. A minimum of 4 ppm will be held now. The liquidator should be in Saturday.
Thanks! Tim

 

[pwrstrk]

Inexperience mainly. I see from the chart that 4 is the minimum. A minimum of 4 ppm will be held now. The liquidator should be in Saturday.
Thanks! Tim

Just to clarify, you don't want to hold 4. That's the min you should never go below. Target 7-8 and that will allow for FC burn off during the day so you DON'T fall below your min. ?

 

[TimTucker]

Thanks! Target of 7 never lower than 4.

 

[jblizzle]

Well, target whatever you have to so that it never drops below 4ppm (AFTER you finish the SLAM process). 7-8ppm should be a high enough target. If you are losing more than 3-4ppm every day, then something is going on.

 

[chem geek]

I have a mostly opaque cover on my pool and if the cover is not opened so no exposure to sunlight then even at 88ºF the chlorine loss is less than 1.0 ppm FC (closer to 0.8). A loss in most outdoor pools of 2 or 3 per day (at normal FC/CYA levels, not SLAM levels) is more typical when the pool is exposed to sunlight, but that is not normal in a covered pool nor for an indoor pool or any pool not exposed to sunlight and without significant bather load. I would say that your chlorine loss rate is on the high side and that something is consuming that chlorine in your pool.