Got the CYA Standard and CH Standard, still have problems testing

[MNiels]

I’ve been using TFP methods and TF-100 test kit for 3 months now and still have difficulty with the CYA and CH testing. I test these weekly because we have new plaster, and there’s so much helpful information on this site, so you’d think I’d have it figured out by now, but I want to be sure I’m doing this right. I finally ordered the CYA Standard and CH Standard solutions, thinking it would help me interpret the test results, but I still have problems with both tests and hope I can get some guidance.

(1) When I tested the CYA Standard, which should read 50 ppm, I read it as 40; even at 30 the black dot was sorta visible but arguable (hubby and I disagreed at 30). We repeated the test a few times and tried looking at it in different sunny spots, inside the pool screen and out in the yard, but with the same result. The pool water test, done in the same time frame, was about the same – arguable at 30, fuzzy but visible at 40, a close match to the standard, which means 50. So, should I adjust my interpretation and assume my pool CYA is 50, and calculate my chlorine needs based on 50? I’m ok with that but not sure what I’ll do when the CYA varies from this reading – I’ll be guessing. I’m fairly sure we followed the instructions correctly, and have tried tips and tricks I found here – any suggestions?
(2) If I misinterpret my CYA and over-dose on the FC, will it hurt anything, besides being wasteful?
(3) I worried that an erroneous CYA measurement would affect the CSI calculation (I check this with my daily testing). But playing around with Pool Math, it looks like a CYA difference between 30 and 50 doesn’t affect the CSI calculation terribly, is that correct?

(4) The CH Standard testing was delightful, a very crisp and clear change from definite pink to definite blue, exactly at 200 ppm. My pool sample, however, looked anemic by comparison, very pale pink and VERY pale blue (nearly colorless), an almost imperceptible change with no change in color intensity even after adding several more drops of reagent. I do use a Speed Stir. I’ve been interpreting my CH as 200 ppm, but is it actually lower? (200 is our target, which is lower than TFP recommendations, but the Wet Edge warranty specifies a CH “not to exceed 200 ppm.”) With new plaster, I want to be sure my CH testing is accurate, and I’m not so sure. Any suggestions?

Thanks in advance for the help! Sorry for the long post - please let me know if this should have been 2 separate ones.

 

[Mr Bruce]

1. Yes if you can't find a way to make the standard obscure the dot at 50, I would just +10 my own readings every time. If you've read through all the other suggestions, I don't have a new one to try.

2. Yes, just being wasteful, not harmful.

3. Correct.

4. I believe, might be wrong, you can add an additional drop of 11, but don't quote me. You could experiment.

Also, re-reading the extended test kit directions, I just realized my reagent is expired (stained bottle) :/

 

[jblizzle]

4. You can certainly add more of the dye. I do the CH with 10ml of water, 10 drops, then 3-4 drops of the dye, then count drops until the last drop causes no further color change and don't count the last drop. Each drop is 25ppm.

Since you CH is lower, you could use 25ml of water, 20 drops, and then 5+ drops of the dye, count and each drop is 10ppm.

 

[mikemass]

Your description of having trouble reading the CYA matches my description to a tee. I hate that test. And like you implied, I just shoot for a higher FC to make up for any error in my CYA interpretations.

I am shocked the surface warranty is saying it can't exceed 200. I don't know what Wet Edge is or how it compares to plain old white plaster. But I was always under the impression that higher calcium is better in a plaster pool, to avoid calcium from leaching out of the plaster itself.

 

[jblizzle]

I assume they are suggesting starting at a low CH for start up and that it will then rise as the plaster cures? Who knows what the pool industry is usually thinking

Do you have more instructions from the installer?

 

[MNiels]

Thanks for the quick responses!
Mr Bruce, thanks for the reassurances.

jblizzle, I'll try the alternate CH test method tomorrow.
*Yes, this was the 28-day start-up instruction on CH level, which the warranty references. They didn't provide any instruction past the 28-day start up. Is it time to bump up the CH now (3 months)?

mikemass, Wet Edge Pearl Matrix is an aggregate-pebble finish like PebbleTec. I've been nervous about such a low CH but assumed it was different for the pebble surface. Would love to hear more input and would be willing to increase the CH if TFP wisdom supports it.

 

[jblizzle]

If you are out of their window, then I would start following the TFP number recommendations. You do not want your CSI too negative.

 

[MNiels]

Oh, good, I'll recheck CH tomorrow and re-target for 225 for starters. I've been able to keep CSI within the -0.3 to +0.3 parameters, usually around -0.1.
Many thanks!