First Test with TF-Pro and bizarre FC readings?

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longinoa

Active member
Jun 22, 2024
44
Los Angeles, CA
Pool Size
20000
Surface
Plaster
Chlorine
Liquid Chlorine
Okay I finally got my TF-Pro kit and ran the whole panel

One thing that is very interesting is that I got a second set of FAS-DPD option so an additional R-0870 and R-0871. My kids wanted to test so I ended up testing FC multiple times (about 6 because they like playing with the color changes LOL)... The bizarre thing is that with one of the powder/drip combos I got a FC of 16 with the other I got a FC of 24. Each of these tests were repeated twice. I am using a single 500ml dripper bottle to pour from. Has anyone seen this before?
ph ~ 7.2
FC = 16 (second measure was 24)
CC = 1
TC = 17
CH = 275
TA = 130
CYA > 80
 
PoolStored said:

Water Testing Errors - Further Reading

www.troublefreepool.com www.troublefreepool.com
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Yeah I read that. I'm not expecting identical results. But repeatable changes of 3/8ths the sample seems pretty large.

The biggest problem as I see it is I am going to do an OCLT to see if I need to keep slamming. If I can't get 2 back to back results within 1 ppm that's an issue. I'll just make sure and use the same powder and reagent just to make sure.

I don't fully understand the chemistry of titration. Will the amount of powder matter? I've seen anything from 1 scoop, 1 heaping scoop, 2 level scoops.
The 2 different bottles may have slightly different holes so it's not the same "per drop" between them.
 
Do you have a speedstir? If not, consider it. Swirling can be a big issue. Taylor SpeedStir

Your second biggest issue is drop size. Evacuate some air before you invert the reagent. Squeeze VERY slightly, allow the drop to form and fall off under its own weight. It is likely that you are just squeezing the drops out quickly. Drop size matters.
 
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I do have a speed stir, I read enough on here to realize it would be a big help.

I am likely squeezing too much Im gonna re test a few times to play around with it.

Thanks for the tips!
 
So one thing that is confusing:

If I look at TA - it says reduce your PH with acid then aerate to increase ph
If I look at ph it says add 6 lbs 14 oz of borax to increase ph.

It also wants me to add 32 lbs of calcium chloride - that seems like a lot!
 
A CH of 275 is just fine. Test your fill water CH. I wouldn't add more.

You almost NEVER have to raise pH. It will rise on its own.

Manage your pH and ignore TA (test for it, but don't "treat" it). Follow this:
  1. TA > 80: When pH gets to 8.0, lower your pH to 7.6. pH will rise. When pH gets to 8.0, lower to 7.6 again. As you do this, TA will come down.
  2. TA is between 60 and 80. DON'T lower pH to 7.6. It will be fairly stable between 7.8 and 8.0 7.8-8.0 pH is fine.
 

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longinoa said:
If I look at TA - it says reduce your PH with acid then aerate to increase ph
If I look at ph it says add 6 lbs 14 oz of borax to increase ph.

It also wants me to add 32 lbs of calcium chloride - that seems like a lot!
Click to expand...
PoolMath is a calculator. If you give it a target, it will tell you how to achieve it. Don't blindly follow its recommendations.
 
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Not sure what the protocol is for new threads vs posting a continuation ...
I have a few questions about SLAM and measuring.

Since my CYA is 80 it means my FC is supposed to be 31 according to Water Testing Instructions - Further Reading I can use 5ml of distilled water along w/ 5ml of pool water then each drop of reagent is 1ppm. Is there any reason not to do this? seems like 31 drops is preferable to 72.

I am assuming that during a slam folks basically do an OCLT nightly?
 
hmm I am starting to doubt my 5ml measurement...

5ml pool water and 5ml distilled water - each drop is 1ppm right?

Today (in the 5ml/5ml test)
At 0630 I was at 27 FC. Added the amount needed to get up to 31 (or at least I thought)
At 1230 I was at 35 FC
At 1745 I was at 31 FC

The orientation means that my pool is basically in shade starting at 1730 or so. I thought great, only needed to do one chlorine add today lets do an OCLT tonight. I just measured at 2115 (with the full 10ml pool water) and my FC was at 21. I find it very hard to believe that my FC actually dropped 10ppm in 4 hours w/o sun when it was basically stable all day. I added the requisite chlorine to get to slam level and will test again before going to bed.

This whole process is very confusing as to when FC gets consumed vs not I brushed this morning (at 0630) and ran the robot during the afternoon around 1400
 
How precisely are you able to measure 5ml of pool water? If your measurement is off by half a ml, that alone will cause a 10% error in your results -- which at an FC concentration of around 30ppm is +/-3ppm. Couple that with the test's +/- one drop accuracy, plus drop-size inconsistency because you're human, and a swing of 4 ppm seems pretty reasonable.
 
DrewLG said:
How precisely are you able to measure 5ml of pool water? If your measurement is off by half a ml, that alone will cause a 10% error in your results -- which at an FC concentration of around 30ppm is +/-3ppm. Couple that with the test's +/- one drop accuracy, plus drop-size inconsistency because you're human, and a swing of 4 ppm seems pretty reasonable.
Click to expand...
Fair point ... Id say about as precisely as I can measure 10ml ... though the displacement systems that taylor has seem nice
 
In the first post you said that CYA is > 80. If it is > 80, your SLAM target is higher than 31. If it’s >80, but 90 or less, target is 35. If it’s >90, you need to do a diluted CYA test.
 

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