Trying to correct CYA from last season

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kennyjg44

kennyjg44

Well-known member
Jul 23, 2024
88
New York
Pool Size
7000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Autopilot Digital Nano+ PPC2
Pool opened over the weekend (mentioned in a previous post); visible water quality was OK, with good amount of debris to be vacuumed (hopefully today). Added DE and tested about an hour later (results below). Filter has been running non-stop since.

Last year, I found this group because my FC levels were continually bad, and found that my CYA was waaay too high. That's when I finally figured out the proper way to run the pool (thanks to you all). At the end of last season, I drained the pool down quite a bit before covering, and subsequently pumped a bit more water out trying to keep water off the cover. Neverthless, it looks like my CYA has over corrected, and I want to be sure to properly address this level (and all others) so as to not end up in the same predicament...

Initial Chemical Test:
FC - 0.0
CC - 0.0
pH - 6.8
TA - 60 ppm
CYA - 45 ppm (was over 90 last year)
CH - 150 ppm
Salt - 1800 ppm

I added 1/2 gallon of 10% chlorine after this test and water did visibly improve within 12 hours. I have not added anything since, as I wanted to check here about the CYA (and waiting on my reagent refills for FC testing). SWG is not yet engaged.
 
With a salt water pool you will want your cya to be between 60-80. In Indiana I try and keep mine at 70 and my FC at 7. Yours is 50, you round up to the nearest 10. Leave it at 50 for now and add your chlorine. Do an OCLT based on 50 cya, and if you pass, then slowly raise your cya to 60. I wiggle my cya up to 70 during the hottest part of the summer to avoid running my swg at too high of a percentage.
 

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Thanks for the info! So you are saying, add chlorine first, complete the overnight test (to make sure not being consumed by algae), and the increase CYA a bit at a time.

Should I add chlorine for FC levels at 50 (3-8) or 70 (I'm usually trying to be 7-10) ?
 
Increase your PH to 7.2
Increase your Chlorine to between 6-8 when the pool is shaded this evening and test.
Test again in the morning before the sun hits the pool. If the chlorine maintains, start increasing your cya up to 60.
Yes, you’re making sure there are no organics consuming chlorine in the water before increasing cya. The higher the cya, the more chlorine the pool will need if you have to SLAM.
 
Just to update -

FC fell from 4.0 to 3.5 overnight; I don't know if thats considered much of a loss, especially since my pool starts getting sun at 6AM, and I tested at 9AM. Still trying to get it up to the 6-8 range. We've also been inundated by the maple tree spinners the last 48 hours, so that is probably moving my numbers slightly.

I'll vacuum tonight and add enough chlorine to try and get to the FC to 8.
 
Don't just try to get to FC 8.
  • Test FC.
  • Use PoolMath to calculate amount needed to get to FC 8.
  • Add that amount of chlorine.
  • Test 30 minutes later to see if you attained FC 8.
  • If needed, add more chlorine to get to FC 8.
  • If you add more, test again in 30 minutes to see if you achieved your FC goal.
  • Rinse, repeat as needed.
If you've first calculated addition isn't attaining the calculated goal, chances are either your liquid chlorine is weaker than the percentage you have set in PoolMath or your pool volume is larger than what you have set in PoolMath.
 
OK, not sure what to make of this pattern.

After vacuuming pool yesterday, I tested FC = 1.5ppm. I added enough liquid chlorine to raise the FC to 8.1. This was done after the sun went down.

This morning's test was FC = 6.0; a bit lower than expected.

Either I am losing FC overnight, or my PoolMath calculations are incorrect (though last year they were accurate). I suppose it's possible my liquid chlorine has lost some potency as well.

Best way to tell?
 

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This is essentially what I have been doing; SWG has not even been turned on yet. But last night I didn't do a 2nd test at night, so will attempt to do so tonight (though we have rain coming).
 
Add chlorine, test 30 minutes later to verify that you reached your projected FC.
If you didn't reach projected FC, either your chlorine is weak or your pool volume is off.
 
OK, so attempting to follow instructions exactly but right off the start I see an issue. Added enough bleach to take FC from 5.5 to 7.9 (+2.4), but FC only increased by 1.0 after 30 minutes. Reagents are new, filter running non-stop, using same testing techniques as last season.

FC 5.5 at 6pm
+ 2.4 at 6:04pm (20 oz of 10%)
FC 6.5 at 6:34pm
 
What is the date on the liquid chlorine?

It doesn't matter if you hit your target or not what does matter is that
1) you have a valid reading above 3 to start the night, and
2) the first test for OCLT is AFTER sunset and
3) your test in the morning is before sunrise.
 
Last edited:
PoolStored said:
What is the date on the liquid chlorine?

It doesn't matter if you hit your target or not what does matter is that
1) you have a valid reading above 3 to start the night, and
2) the first test for OCLT is AFTER sunset and
3) your test in the morning is before sunrise.
Click to expand...
We haven't had any sun here all day, clouds and overcast. I'm guessing there is still enough UV to eat up chlorine, though. I'll take the reading tonight, but sunrise is 5:30a and it'll be raining, so not sure I'll get to that one on time.

Can I shelve this until next week?

I don't see anything resembling a date on the chlorine box, will check again
 
Got it.

Interestingly, after dark FC = 7.5; closer to what I would have expected earlier. Maybe my water doesn't fully circulate in 30 (though my pool is small)
 
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