CYA Surprise

Wobblerlorri

Bronze Supporter
Well, my husband, a noob at testing, discovered I was doing my CYA test horribly, horribly wrong.

I have the Pentair kit, and I thought my CYA was 40 ppm. I taught my hubby how to do CYA, and he comes up with 100 ppm. WHAAAA...?

So we tested again. Same result. What in the world? I had just added enough the bring it up to 40! Then he showed me my error: I was reading the amount at the TOP of the plunger, rather than through the tube at the waterline!

EGADS!!! MY CYA IS AT LEAST 100 PPM!!!!!!!!

Since it's so close to the end of summer, I'm going to leave it alone. I'll be draining it below the skimmer anyway to winterize it. What puzzles me, though, is that my chlorine has been acting as if I have 40 ppm CYA all season. Target of 7 ppm, responds accordingly to appropriate additions of chlorine, even the SLAM and mustard SLAM I did worked perfectly. How can that be with such a high CYA?

The mysteries of pool chemistry. I may go ahead and order a TF-100 and test CYA against that kit. Just to see, you know. I'm going to test again with the Pentair kit and a dilute sample to see just how much I need to drain. My luck, it'll be a complete replacement...
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,472
Portland, Oregon
I just watched this, and it appears you're right.

I don't know what to say. Can't say why your SLAM worked so well. But maybe it didn't really and your 24hr at mustard level just did the trick and you didn't actually have mustard algae. High FC levels will eventually clear a pool even if not at SLAM level, it just takes much longer and iirc, you didn't actually have a green pool in the first place.

I wouldn't buy a whole TF-100 right now if you don't need the reagents. They will just expire sooner than you can use them. Getting CYA reagent, the bottle, and the tube only will be enough to verify your results.

But after watching the video, I see no reason to doubt them in the first place. Waterline is where you're supposed to read it.

Doh!
 

Lilypad

Bronze Supporter
Nov 12, 2016
181
Plano, Texas
I have the same Pentair test kit from a few years ago. Picked it up to do a fast CYA test, instead of taking my tackle box with the TF100 in it, and forgot that you read AT the water line in the tube and not the top. So when
I got over the crazy low CYA number it showed, I retested with the TF kit and all was well. Don't feel bad, we all have stuff like that happen!!! 🤪
 

Wobblerlorri

Bronze Supporter
Just ordered the T FT CYA reagent, mixing tube, and viewing tube. Let's see how badly I can screw THIS up...

went back over my records, and I've only added enough to bring my CYA to 70 or 80. Don't know how it got up to 100. It is a mystery...
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,472
Portland, Oregon
When I think about your saga...

Your Pentair result is so... potentially accurate.

The TF-100 tube will likely produce the same result.

I watched the video. Water line is the determining factor.
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,472
Portland, Oregon
BTW, forgive yourself!

I added 20ppm CYA because I'm stupid and apparently forgot 1c didn't equal .6c.

The world will not end.
 
Last edited by a moderator:

Wobblerlorri

Bronze Supporter
Checked the FC/CYA Chart chart, and upped chlorination to 13 ppm. Also discovered a math-based way to calculate your CYA based on how much you've added over a time period.
  1. add up all stabilizer additions in ounces for a given time period
  2. divide by 11, the amount of CYA in 10 ppm
  3. multiply by 10 to correct from 1 ppm to 10 ppm
My current CYA is about 98.4 ppm. Not a wonderful number, but a fun thing to figure out. I guess.