TF-100 and the CYA test

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napkin41

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Mar 4, 2018
60
Prosper, TX
Hey all,

Just got my TF-100 test kit (with speed stir :cool: ) and I tried my hand with all the tests.

I'm happy to say that I love this kit, and I feel like I can really trust and reproduce the results!

The CYA test though, that one seems really "subjective" to me and I was having a hard time with it. I found that as I did the test, I'm squinting into the bottom of the tube and thinking to myself man, I can still see that dot! I don't know if it's maybe because I did it indoors under a decent amount of light as opposed to outdoors "with my back to the sun."

Anyhow, I was reading about 20-30 CYA, and since I had leaned on the pool store this whole time up to now, they were telling me my CYA was in the 50-60 range. I think I'm just gonna go ahead and believe their numbers until I can do this test a little better.

Do you guys have any tips for performing that particular test, or is there perhaps another product that measures CYA really well?

Thanks!
 
Glance away then at the tube again.... OUTSIDE!! With the sun to your back. I find it easiest to just squirt the liquid into the tube all the way up to 100, then all the way up to 90, and so on thru the numbers and then do the glance away-look thing. It helps speed up the test and improved my confidence.

It is a subjective test for sure, but with practice you'll feel more confident.

Maddie :flower:
 
You can also pour it back and forth a few times and let your eye take the average until you get better acquainted with it. Outside light for sure......and I don't mean on a cloudy day either!
 
This is my personal go-to CYA reference:
Proper lighting is critical for the CYA test, so you want to test for CYA outside on a bright sunny day. Use the mixing bottle to gently mix the required amounts of pool water and R-0013 reagent, let sit for 30 seconds, then gently mix again. Recommend standing outside with your back to the sun and the view tube in the shade of your body at waist level. Then, begin squirting the mixed solution into the skinny tube. Watch the black dot until it completely disappears. Once it disappears, record the CYA reading. To help the eyes and prevent staring at the dot, some people find it better to pour & view in stages. Pour some solution into the viewing tube, look away, then look back again for the dot. Repeat as necessary until you feel the dot is gone. After the first CYA test, you can pour the mixed solution from the skinny view tube back to the mixing bottle, gently shake, and do the same test a second, third, or fourth time to instill consistency in your technique, become more comfortable with the testing, and validate your own CYA reading.
Click to expand...
 
Awesome, thanks everyone for the help. I'll have to try it again on the weekend perhaps. My pool gets my attention after work when the sun is setting, but it does look like lighting is the key. I'm pretty sure I'm probably in the 50-60 range, I was trying pretty hard to see that dot which made me fill up the tube more and more.
 
Just do the glance, if you can't see it right at first right when you glance in, that's it. The glance method is better for consistency, pour in every 10 as the scale is not linear so trying for halves is just guessing.
 
As you learn and read more on this forum, you will find about the LAST thing you should do is trust pool store test results. Believe in your test kit and believe in your ability to use it.
 
Just wanted to give you guys an update. I became more intimate with my CYA test, and I think I feel better about executing it. It was bright and sunny today, so with my back to the sun, I tried the test again. I filled the tube at increments of 10, put it down at waist level as I looked away, and then glanced at the dot. If I felt it practically wasn't there, I stopped the test.

It was 40 each time, which is a bit lower than I expected, but feels right. I have been adding bleach and targetting chlorine for CYA levels of 60, and on these cool, sunny days, I was losing about 3 ppm over the course of 24 hours. Seemed like a lot to me without it being summer and all, so in my mind that kinda justifies a lower CYA level than I thought.
 

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A tip on the CYA test, if you ever get a result that's between 2 number, always round up. IE: if its between 30 and 40, round up to 40 and use this when you calculator your new FC target. You don't want to end up in a situation where you FC falls below the minimum for the CYA that's actually in your pool, cuz then you'll risk an algae bloom. [FC/CYA][/FC/CYA]

Also, I live in GA and we've got similar temps to Prosper, Tx right now. My pool is in the sun from sunrise to sunset and losses around 1ppm a day right now. An Overnight Chlorine Loss Test might show that you've got an algae bloom starting already.
 
I'll do an OCLT tonight. Two days ago CC's were at zero. I'll check again this evening.

Is FC loss always the same rate regardless of how much FC you have in your pool? If my FC was at 80, would I still lose it just as fast as if it were at 7?

And, in North Texas we have been having some bright sunny days and 60-70 degree weather. So, I'm not sure if that also may suggest why I'm losing about 3 ppm.

- - - Updated - - -

Also, I live in GA and we've got similar temps to Prosper, Tx right now. My pool is in the sun from sunrise to sunset and losses around 1ppm a day right now. An Overnight Chlorine Loss Test might show that you've got an algae bloom starting already.
Click to expand...

Oh, so an OCLT is an indication that algae may be forming? If that's the case, won't I start seeing some CC as the FC engages the algae in battle?
 
As a general rule of thumb, the higher the FC, the faster it degrades. If you bring your pool to shock FC level, with no algae or organics in your pool, it will drop much faster than if it had started at the proper FC level for your CYA.

During the nighttime hours, with no sun to breakdown the FC, you should lose a very small amount of FC. If there's algae or other organics in your pool during the test, you'll lose more FC. Test your water an hour after sunset, and then again before sunrise. If you lose 1 FC or less during the night, your pool is clean of algae. If you lose more than 1 FC during the OCLT, then there's likely algae or something else in your pool that the chlorine is reacting with. Also, with the test, make sure you're doing the FAS/DPD chlorine test, not the OTO test (don't use the one attached to the pH test).
 
It's just a rule of thumb, once you get your pool figured out you will know what's too high and what's not. Overnight test rules out uv. Uncovered outdoor pools lose cc's because of the sun, so it can be hard to catch them during a day test.
 
Ok all.

I'm considering opening a new thread since we went from "the TF-100 CYA test" to "why is Napkin losing so much chlorine during the day," lol.

But, at any rate, I conducted the OCLT last night and I didn't lose any chlorine. Just to give complete transparency, this is what I did:

1. Just before sundown, I added my daily dose of chlorine, because I get home kinda late. (Target 7 for CYA of 40)
2. I took an FC reading 20 minutes later, 6.5ppm
3. Just to be absolutely sure everything was mixed, I took another FC reading when everything was completely dark outside. 7ppm
4. This morning, just as there was daylight but the sun hadn't come up yet, I took a reading and got 7ppm.

So, it doesn't look like there's anything in my water that the FC is fighting. Here's a list of factors that I want to share that may or may not contribute to losing about 3ppm over the course of the day:

1. My neighborhood is new and growing. Right behind my backyard fence, bulldozers are leveling and grading an entire new patch of what will be more houses. This land was previously farm land.
2. My plaster is still curing slightly? It's going on 7 weeks old, I still get dust when I brush daily and ph rises slightly over the course of the week. (I don't think this would eat FC.)
3. Going into spring, I am skimming bugs off the top of my pool, and I found a really cool spider just chilling underwater in one of my skimmers. Bug load is going up? lol
4. We have been having some sunny days with temperatures in the 70's.
5. Also, literally Monday was the day I became a TFP'er and pulled out my tabs to forever use the TFP method. FC was a roller-coaster before I established my new routine. Saturday I discovered my chlorine was low, so I used the Sodium hypo that the pool store gave me to "shock" it up. Sunday it was high. Monday I got my brand new TF-100 kit and began my bleach regimen.

So, sorry for the novel, but I will continue to measure FC each evening and add bleach to target 7ppm, and I'll see where it goes from there.
 
Elewi2, yeah, I definitely had that very picture pulled up on my computer as I was conducting the test, lol. even in that last picture you can see some semblance of a black dot. Once I convinced myself that the dot will never be 100% obscured, I think I started to get a pretty good idea of how to do the test.

(Hopefully I'm not stopping the test too early now. I'll keep practicing, lol)
 

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