Precision affecting OCLT ability to pass?

[JMezei]

Greetings!

We got our gunite pool finished in late May and I confess to relying on pool store too much in the beginning. I think using their Stain & Scale Remove and letting it consume all my FC caused me problems. No obvious algae, but cloudiness and my inability to keep FC led me to a SLAM. (My research in TFP is also what clued me in that my target FC was way too low.).

PoolMath told me to shoot for a SLAM FC of 24ppm for my CYA of 60. I maintained the levels from 8/24 thru this morning. I passed the clarity and CC tests easily, but I lost 1.5ppm FC last night. I knew I wouldn’t have enough R-0871 to get through another day’s worth of tests, and I found this blurb that made me wonder if I’d ever show a <1ppm loss.

• The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.

Since I was measuring up to ~24ppm (48 drops) at the nighttime and morning OCLT readings, wouldn’t the precision be limited to up to 4-5 drops, which could be more than the 1ppm range I’m trying to meet? I hope that question makes sense.

 

[PoolStored]

THOUSANDS of SLAM participants that can pass OCLT at elevated levels. Hold your bottle vertical. Squeeze drops slowly, and let them fall under their own weight...don't "force" them out. If you have speed stir, even better. So, no...no "skoosh" room.

 

[PoolStored]

Oh, and Welcome to TFP!!!

 

[JMezei]

[wondering what was redacted )

Well, shoot. I’ll have to wait till I get more reagent and then start all over, I guess. I tested lots of times throughout the days, so went thru that bottle faster than expected.

For my future SLAM(s), I’d Like some guidance. One night, I did the drop test and got an FC of 19 so added 78oz of 10% at 7:25pm, and when I did the drop test again at 10:50pm, the FC was up to 25 (even though I had aimed for 24). The next night, FC was 20 at 9:30pm so I added 60oz, but then at 11:50pm, it was again high at 25. These were the only readings at night (besides the early morning OCLT readings), so is it likely because no chlorine was being consumed by UV? I was just surprised that my pool math didn’t seem to work quite right at the same time of night, twice in a row. Is it possible that my FC dropped more overnight because it was already starting a bit higher than SLAM level (I read FC fades faster at the higher levels)?

 

[JMezei]

A

THOUSANDS of SLAM participants that can pass OCLT at elevated levels. Hold your bottle vertical. Squeeze drops slowly, and let them fall under their own weight...don't "force" them out. If you have speed stir, even better. So, no...no "skoosh" room.

Waiting on my speed stir, and I’ll try to improve my drop angle going forward.

 

[proavia]

For my future SLAM(s), I’d Like some guidance.

Best guidance is to manage your chemicals according to TFP protocols. Chances are, if you are consistent, you will never need to SLAM Process again.

Your measured FC being a point or two higher/lower than what PoolMath suggested can have to do with the chlorine being a little more/less strong than indicted on the bottle and/or your pool volume being more/less than you think.

The FC being 1 point higher than SLAM level shouldn't affect the overnight drop.

Honestly, quit overthinking it and follow the SLAM Process to the letter - no shortcuts.

 

[PoolStored]

I’d Like some guidance.

If you overshoot, add 500 gallons to your pool size in pool math. If you undershoot, reduce pool size by 500 gallon in pool math. Rinse, repeat until you get your expected result with your chemical addition.

 

[Bperry]

[wondering what was redacted )

Well, shoot. I’ll have to wait till I get more reagent and then start all over, I guess. I tested lots of times throughout the days, so went thru that bottle faster than expected.

For my future SLAM(s), I’d Like some guidance. One night, I did the drop test and got an FC of 19 so added 78oz of 10% at 7:25pm, and when I did the drop test again at 10:50pm, the FC was up to 25 (even though I had aimed for 24). The next night, FC was 20 at 9:30pm so I added 60oz, but then at 11:50pm, it was again high at 25. These were the only readings at night (besides the early morning OCLT readings), so is it likely because no chlorine was being consumed by UV? I was just surprised that my pool math didn’t seem to work quite right at the same time of night, twice in a row. Is it possible that my FC dropped more overnight because it was already starting a bit higher than SLAM level (I read FC fades faster at the higher levels)?

There’s too many variables for pool math to guess right. In the future, you don’t need to test again after you added chlorine to bring it up to SLAM level at night (unless you’re doing a OCLT in which case it’s required) You’ll be testing again in the morning anyway. You might do it a couple times at the beginning just to know if your calculations are close enough though. Sun, organics, water volume, chlorine concentration, temperature, sunlight and probably some other unknown environmental factors all play apart in how chlorine reacts in water so don’t sweat it pool math accuracy too much. The OCLT is a good tool to use and was designed with all that taken into account.