Confused By pH & CYA Tests in FAS-DPD Test Kit

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LarryG

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Jun 3, 2014
25
Lee County, FL
Hi, folks! Need your feedback / advice.

Received my very first test kit today. Results were:

FC= 6.8
CC= 1.2
TA= 80
CH= 360

But when I did the pH test, the color of my water didn't match any of the guide colors on the comparator tube. My sample was pinker / darker... nothing close to the guide colors. Repeated the test, and achieved a similar result. (I'm not color-blind, but also had the wife take a looksy and she thought the same.)

Also, when I did the CYA test, the sample volume didn't reach any of the CYA values on the comparator tube. My volume was way below the first mark (100).

So I got out an AquaChek test strip, and got results indicating the Total Chlorine was 5 to 7, FC was 3 to 5, pH > 8.4, and TA was 100.

Then I decided to take a sample to the local Leslie's for comparison, and the store manager (who has mentioned he has significant experience) came up with:

FAC= 5
TAC= 5
CH= 310
CYA= 60
TA= 110
pH= 7.6
TDS= 1300
Phosphates= 0

Water looks good. Have had lots of rain in the past week.

A week ago, I emptied the inline chlorinator (chlorine levels were very high), and decided to go with the TFP method.

I'm a new pool owner (18 months), and was using the trichlor tabs up until now... without apparent issues.

How did I screw up the pH and CYA tests? What do you make of the above? I know the Leslie results seem pretty good.

All your thoughts / comments are appreciated.

Thanks!

/Larry
 
Re: Confused By pH & CYA Tests in FAS-DPD Test Kit

Larry,

Welcome to TFP. What test kit do you have? I only have experience with TFTestKit. If the pH was a "super brite pink" brighter than the 8.2 on the guide chart than it is probably above 8.2. Others much smarter than me will be here shortly

- - - Updated - - -

I recommend that you add your test kit to your signature. Helps out a lot.
 
Re: Confused By pH & CYA Tests in FAS-DPD Test Kit

Pretty hard to mess up the pH test. If I was in your position, I would use pool math to calculate how much muriatic acid to lower pH from 8.2 to 7.5. Using 9000 gallons, PoolMath recommends adding 14 oz. Do it yourself to see what you get - good to learn this tool because it will quickly become your friend using the TFP method.

Whatever it comes up with, go ahead and add it with the pump running. Wait 30 minutes to an hour to test again. You may not hit 7.5 because it was probably higher than 8.2 to begin. If it comes back at 7.8, I would just leave it alone. If it is 8.2 on the second test, add the recommendation again and retest again - 30 minutes to an hour later.
 
It doesn't sound like you screwed anything up, just misinterpreted the results.

Your pH test indicates very high pH, as jagger said. You will want to bring that down.

Your CYA test indicates very high CYA levels, judging by your description I would wager several hundred which is much too high to manage properly. You are going to have to start planning a very significant water change based on that.

And your Leslie's results from the experienced manager just goes to show, their test isn't worth the money paid for it.
 
(Thought I just responded, but don't see it.)

Man, you guys are fast! Just sat down to dinner, and when I finished... bada-bing, there were three replies. Thank you.

Using the Taylor K-2006 test kit.

Just experienced another downpour, so will start making adjustments in the AM.
 
+1 ^ probably very high CYA..

You can determine how high using your test kit:
  • mix 1 cup pool water with 1 cup tap water (has no CYA). Mix or stir well.
  • use this sample to do the CYA test just like you did it the first time.
  • If you are able to fill past the 100 mark on the test cylinder this time, then take that result multiply by 2 and that is your CYA level.
  • If your level still is over 100 then mix 1 part pool water with 2 parts tap water.
  • Continue with the test as before... if you get a result lower than 100, then multiply that number by 3 to determine your CYA level.
  • If it is still over 100... (It has happened... :eek: last week someone had their CYA=540!) then go on to mix 1 part pool water to 3 parts tap water and multiply the result by 4.
  • and so on...

At best the CYA test has a margin of error of +/-10ppm... if you have to dilute, then you will be increasing that MoE by 5-10ppm for each dilution you must do. You can minimize the MoE increase somewhat by measuring the "parts" of pool water and tap water very carefully, so that they are as exact as possible.-- but honestly, if your CYA is over 100 anyway, +/- 20ppm isn't gonna change a whole lot. You will still need to drain and replace water, or manage a pool with higher baseline FC to compensate (only recommended if water replacement is NOT an option, i.e. California drought restrictions)

BTW... the Leslie's "experienced" manager may have gotten inaccurate results for any number of reasons... :suspect: chief among them: poor testing technique (because they are rarely taught that technique matters).

I would bet dollars to donuts that the manager had the view tube up on the raised counter, adding the solution to the test tube in quick "squirts" and not drop-by-drop, and that he was looking into it under fluorescent lights inside the store... right?:uhh:

Taylor, the company that makes the test, recommends:
  • that the reading be done outdoors, in full sunlight;
  • standing with your back to the sun, so your body creates "shade" over the test tube
  • view tube held at waist level, looking down into the tube while adding the solution, drop by drop.
  • stop adding the solution as soon as the dot becomes completely obscured. If you think you still see it, add another drop. Sometimes jiggling the tube helps you figure out if you are seeing the dot or a shadow.
  • Important: You can pour the solution out of the test cylinder back into the dispensing/mixing bottle and restart, or just try again, to see if you get the same result. If it's a little different, you can average the two numbers.

    You can also add the solution back into the mixing bottle and try doing the test different ways if you want to see how testing indoors or with the tube held up closer makes the result different.

Try the CYA test again using the method and instructions above, and come back and tell us your results.
(BTW... if I were you, I would probably start with the 1 part pool water to 2 parts tap water, to minimize the chance of having to test again. Your level is surely over 120, and you would get to that at the 1:2 dilution, if you ended up filling the test tube to the 40 mark and multiplying by 3...
Keep in mind, that yours may be higher still-- my suggestion is just a place to start.)

Good Luck! :flower:
 
Added 12 oz of MA early this morning. Checked when got back home in the afternoon, and pH was at 7.6... great!
Was gonna re-check CYA, April (using your dilution method)... but now getting another downpour... lately just about every late afternoon it rains here.
Thanks again to all for all the great tips... will be saving them for the future.
 

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Yeah, a cheap pump will be your best bet.

Although a major drain would be the most efficient, since you are in Florida and likely have a high water table you will need to be careful. We had a recent news article posted here (that I can't seem to find at the moment) of a pool completely floating out of the ground during a heavy rain, it can happen even to a concrete pool. If you don't know your water table and have been having a lot of heavy rain then it might be a good idea to only drain a couple feet at a time. A slower process but a pool popping out of the ground can do some real damage. Like you guys are saying too, if you can somehow time it to a good rainfall and use mostly rain to fill it then it might work out great. Reroute those downspouts!
 
Thanks for jumping in guys.
Checked the CYA today and it was a lot lower than my previous reading... much closer to the 100 mark.
Just finished draining 10% (900 gallons). (Got pump at Lowe's for $98 -- 1/3 HP -- worked great!) Replacing water as I type.
Rained again today, and daily rains are expected through the end of the weekend, which will help with dilution. Planning on additional cautious dumps over the next few days.
Will be checking pH and chlorine daily and making adjustments.
Water continues to look fine... fingers-crossed!
 
Yesterday I added MA to bring down pH to 7.4, and chlorine to raise FC to 10.
Tested today and achieved the above values. Tested CYA (using the 1 to 2 dilution method) and it measured approximately on the vial 32, which converts to a CYA of 96. So things are going in the right direction.
Will do another conservative drain later. Been having a lot of rain here all this week.
Will continue to post results.
Thanks!
 
Replaced another 1500 gallons last evening, then had some more rain last night.
Checked and adjusted pH this morning. CYA is at 82. FC is 4.5. Added chlorine to achieve FC of 9.
Water has been looking great!'
Will continue working to get the CYA below 70.
 
Larry,
For CYA, just round up to the next higher number.
The scale isn't linear... it's logarithmic... that's why the numbers get further apart the higher up the tube you go. So, that means you can't accurately estimate the values in between what is marked, unfortunately.

I know it seems sort of counter-intuitive to think that way. Especially when you are trying to get your # down, it is doubly hard to round up. But if you don't, you risk having your FC end up just a bit too low... and then the next thing you know, it's an algae party in your pool. :rolleyes:

I must have neglected to mention that in my "tips" before.... sorry

Great job getting it down so far, though.
Trust me, your pool will be much easier to manage with your CYA at a decent level.
 
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