High CYA - what to do first

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Your numbers are an OCLT start of 14.5 to 17.5 ppm FC and then in the morning your numbers are 12.5 to 15.5 ppm FC, which shows a range of 0 to 5 ppm FC loss.

The range of drops suggests testing challenges; a range of six drops is unusual. It's normally easy to tell when there is no pink remaining in the water.

My suggestion of 8-10 was because it might be a bit easier to do the testing. Anything you can do to collect water and test consistently will improve your consistency between FC tests. The same person doing the test will usually have less variation than the test accuracy specification. A few things to keep in mind include: pump running for 15 to 30 minutes prior to sampling; sampling from the same place and depth; testing right away; same fill level in tube; adequate DPD powder; slow (1 per second) drops fully formed before dropping away from the bottle; sample being swirled, slowing down to allow mixing toward the end of the test; white background; that type of thing.

8-10 also works because if you need to resume the SLAM, you really haven't lost much SLAM time.
 
It's interesting how people see things differently. I can't imagine how expected accuracy would not consider the test method.

I forgot to mention holding the bottle vertically above the test vial when letting the drops form. That should have been in my list of tips.

When there's no algae in the pool, you should see zero loss of FC in the OCLT test. The 1 ppm tolerance allows for typical challenges.
 
My SLAM is over. The FC hasn't dropped overnight for the past few days and now I'm working on bringing the CYA up to around 70-80. My plan is to then get the TA to around 60 from its current 130.

Thank you for the advice, needsajet!
 
needsajet,

what is your CYA at? I may have overshot my CYA goal a little bit (this test is ridiculous!) to about 90-100. Temps are going over 100, pool in direct sun, so I might need to actually leave it there.

But with an SWG, what should my FC be? 8? Or higher? The chart doesn't go that high for SWG.
 
Yeh, that test is a pain!

When you're at 90 ppm CYA or above, do a diluted test to verify. It's described as point 8 in: Pool School - CYA

I like a target of 10% FC, so if I was at 100 ppm CYA I would target 10 ppm FC. If minimum FC was important to me, I'd then ease it down to 5-7 ppm FC over time, keeping an eye on the pool to be sure it's working. Either way, I'd treat 5 ppm FC as a bare minimum for 100 ppm FC.
 

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Problem is mainly that I don't know if I'm over 90ppm ;)
I'll do a diluted test to verify, though.

I don't have a problem practicing better safe than sorry, but how high can I go with the FC before it creates an issue for swimmers, robot, etc.?
 
bizzle said:
I have an established, inherited pool that has lived on pucks for likely decades. The CYA is currently off the charts. I have a TF-100 kit but I'm not sure which chemical to bring under control first before I start up my intellichlor. Should I aim for making sure my pH is correct before I drain and retest CYA or can I just drain and fill and get my CYA in a ballpark range before going through all the tests?
Click to expand...

The solution to pollution is dilution
 
As long as you don't need to SLAM, it's fine to run the pool at high CYA. At 7.5% to 10% FC/CYA in ppm, you have way less active chlorine than most commercial pools. The FC (free chlorine) measurement includes all the chlorine tied up with CYA (around 95% of the FC), and only around 5% of the FC exists as active chlorine which is what does the sanitizing, and the part that can cause things like elastic in swimsuits to deteriorate.

The pool is perfectly safe for swimming all the way up to FC at 40% of CYA (the shock level), or around 40 ppm FC, at 100 ppm CYA. So 10% (10 ppm FC at 100 ppm CYA) is way inside the safe territory, and not harmful to swimmers or equipment, and is roughly equivalent to a non-CYA commercial pool at somewhere around 0.12 ppm FC, yet they typically run at 1-3 ppm FC, and therefore way, way more active (some call it the harsh part) chlorine.
 
Just when I thought I had it dialed in...calculating the SWG run-time/% is killing me!

I have it scheduled to generate from 8am to 8pm at the following percentages:
Left for the weekend: Friday, Saturday, Sunday (91F) 12hrs@100%FC 6 (Friday morning) > 9 (Monday morning)


Monday 12hrs@75% 81F
10pm 9


Tuesday 12hrs@50% 73F
10pm 9.5


Wednesday 12hrs@25% 76F
10pm 8


Thursday 12hrs@45% 86F
10pm 7


Friday 12hrs@47% 97F
10pm 7


Saturday 12hrs@48% 104F
10pm 5.5
Click to expand...
It's going to be 102-106 the rest of this week.

Is my CYA not high enough even at 90-100 for these temps?
 
You can do an Overnight Chlorine Loss Test anytime to rule out algae, or detect algae.

12 hrs at 70% is around 3.8 ppm FC per day. I'd try that for a week and see what readings I got. The FC level will not rise very quickly, perhaps 1 ppm per day if there's no algae.

Just double-checking... be sure the flow rate is high enough that the SWG is always on when it's meant to be. I doubt very much that's an issue, but I can't remember if it's been ruled out.
 
I've done a couple OCLT a couple times just to rule that out. There have been a time or two when the pump lost just enough flow to not generate, but that was before 10am and I ran the super chlorinate for 3 hours to compensate.

So looking at the numbers above, I was keeping it right around 9 and then dialed it down to where it was looking like I could keep it stable at 7. But then the heat wave hit (and it's only going to get hotter from here rising to 120-130 in about a month) and the FC plummeted to 5.

I checked it Sunday morning and it was at 5.5 (no drop overnight from the Saturday measurement at 10PM) so I added half a gallon of 10% to bring it up to 9ppm (poolmath called for 88oz...but I now realize I only put about 60oz in). I checked it again at 10PM Sunday night and it was back to 5. Then I bumped it up to 75% per your suggestion (it's running from 8am to 8pm) with a 3 hour super chlorinate (I think it's 100%), which should have closely compensated for the 3-4 hours it wasn't generating that morning.

Last night it was back to 5ppm. It doesn't drop any lower, either (it's 5ppm as of about an hour ago, which was approximately 2pm PST). So should I measure out enough to bring it up to 9ppm again, increase it above 75% generation, lower it to 50% and just run it 24 hours through the night? It seems like the heat, the 14hrs direct sun exposure, and me still not knowing the exact setting it should be at, are just chewing through my chlorine.

The worst part is, am I going to have to be adjusting this SWG throughout the entire year or am I going to have to run it at 100% for the hottest part of the summer? It's going to drink a gallon of MA if so :(
 

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