CYA reading struggles

[ti_chris]

Hi,

I recently reset my pool and have had to adjust my CYA again. I'm struggling a bit with the reading of the levels. ie: At what point does the black dot fully disappear. I'm wondering if I'm not too picky about when the dot really vanishes. The pool store measures my CYA at 58, which seems crazy given that I can't really keep any chlorine in the pool for longer than 24hrs even after raising the FC between 6-8 and the pool is otherwise crystal clear. I've added pictures of my test.

The first pictures has the solution filled to the 40 line
The second at the 30 line
The last image has it filled to the brim of the container (technically not marked)

I can personally see the dot in every one of them, although it's extremely faint in the last one and could concede that it's probably close enough to that level. Thoughts? I am looking correct in thinking I'm < 30?

 

[DrewLG]

Calibrating your eye against a known reference will help a lot.

Buy this 50ppm CYA standard solution: R-7065 CYA Standard 50ppm (2oz) and mix CYA reagent with the solution instead of with pool water.

Shake, wait a couple minutes, shake again, and fill the viewing tube to the 50ppm line. Look down into it. What you see is the endpoint that you should look for when you do the test with your pool water.

Also see what the dot looks like at 70, 60, and 40 ppm, so you'll have an idea of how much visible difference there is between the measurements.

 

[ajw22]

Accuracy in the CYA test does not matter much. If you are going to error on the CYA test, error on the high side which is why we always round up.

I say the test you posted is CYA 30. Set your FC in the CYA 30 range and move on.

The CYA value is only used to set your FC range. If you error on the high side you use a few more ppm of FC. Too much FC is never a problem, too little FC can be a problem.

 

[setsailsoon]

Yep, I'd call it 30 as well. Filling the tube all the way up so long as you have over the minimum CYA gives you a good idea of what a completely obscured spot looks like. I'd also say don't over-think this test. Look up and down before checking, what you see at first is the right reading. Also, don't try to confirm with pool store test. Their results on this test are notoriously bad. Personally I like the CYA test that comes with the TF 100 because it has a larger dot at the bottom. Seems to be a little easier to read.

Chris

 

[ti_chris]

Calibrating your eye against a known reference will help a lot.

Buy this 50ppm CYA standard solution: R-7065 CYA Standard 50ppm (2oz) and mix CYA reagent with the solution instead of with pool water.

Shake, wait a couple minutes, shake again, and fill the viewing tube to the 50ppm line. Look down into it. What you see is the endpoint that you should look for when you do the test with your pool water.

Also see what the dot looks like at 70, 60, and 40 ppm, so you'll have an idea of how much visible difference there is between the measurements.

Ahh that's super useful to know. I ordered one to get a sense of it. 13$ won't break the bank to be better prepared

Accuracy in the CYA test does not matter much. If you are going to error on the CYA test, error on the high side which is why we always round up.

I say the test you posted is CYA 30. Set your FC in the CYA 30 range and move on.

The CYA value is only used to set your FC range. If you error on the high side you use a few more ppm of FC. Too much FC is never a problem, too little FC can be a problem.

Thanks. Makes sense for FC level-setting.

Yep, I'd call it 30 as well. Filling the tube all the way up so long as you have over the minimum CYA gives you a good idea of what a completely obscured spot looks like. I'd also say don't over-think this test. Look up and down before checking, what you see at first is the right reading. Also, don't try to confirm with pool store test. Their results on this test are notoriously bad. Personally I like the CYA test that comes with the TF 100 because it has a larger dot at the bottom. Seems to be a little easier to read.

Chris

Thanks. It's just tricky because a careful eye can almost always spot the dot, but 100% agreed with you. The pool stores used to be accurate when they were using the same Taylor kits, but now they're all using this really crappy technology that adds about a couple dozen drops of water to one spinning wheel that measures everything, but the measurements are pretty inaccurate on all fronts. I guess it sells more chemicals <shrugs>