Testing pH at high FC?

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Jim H.

Jim H.

0
Jun 9, 2014
11
Tucson, AZ
Split by moderator from HERE. Please ask questions in your own thread to avoid confusion. Thanks, jblizzle

It was mentioned in this post that pH can't be tested accurately if FC is greater than 10. Is there any way to accurately detrrmine the pH when the FC is high? I was under the impression that one can't use dilution methods for testing pH.
 
Didn't mean to hijack the previous thread; thanks for starting this one for me. Let me give some background:
Bought the home with pool/spa in April and with zero knowledge of pool care. Let the pool service continue to handle things for a couple of months until I learned what I needed to take over maintenance for myself. I posted earlier about my incredibly high CYA levels. Previous owners were winter only residents who never drained the pool once in the nine years they had the pool and used only Trichlor as the Cl source.
The only test kit I had was an HTH test strip with a max of 300 on CYA levels. My water read over 300 even immediately after dipping the test strip. One of the Mods here put it best when he described my CYA as "insane". I ordered and received my TF100 kit last week and it verified that I was indeed in big trouble with the CYA levels. Even with a 2:1 dilution ratio the black spot in the test vial disappeared after only an inch or so liquid was added. I knew that I had to drain and refill the pool but temps have been and will continue to be over 100 so I was hesitant to drain the pool in such hot weather. Have read that it is definitely not recommended when temps are over 100. We had a couple days of mid-90's temps this week where I live so I took the chance and drained some of the pool overnight. Was only able to get about 6K gal out because I wanted to be sure I could refill the pool overnight while the temps were down. It's still not enough but have verified that the CYA is now "only" at 140 using the dilution method. I want to add MA to keep my pH levels on the lower side (7.2) per suggestions here but now I learn that FC > 10 defeats the pH test, so I don't know whether my 7.5 pH reading is correct or not. FC is currently 13 which is right for the CYA levels that I have. Any suggestions would be greatly appretiated.
 
That high FC makes the pH read higher than reality. If you keep it around 7.8, that might have the pH in range, depending on how high the FC level is .. hard to say really.
 
With FC between 10 and 15 the PH test will read high by somewhere around 0 to 0.3 too high. So you can't really lower PH to 7.2, as that might be 6.9 (not good) but you can keep PH around 7.5 (as the test reads it) and be somewhere around the 7.2 to 7.5 range.
 
I live in Tucson also and had high CYA at one time (around 160). Got it down to 100 which is manageable. One hint, and you may have thought of it, is when a monsoon shower is imminent I drain a few inches out. That way any rain that falls is as replacement water and not just dilution water. I hate to drain too much as I feel bad about throwing water out in our water starved area. It will probably take a year or more to get my CYA in the 50-60 range ( which I feel makes more sense with our extreme amount of sunshine, over 330 days per year, and heat)

I think I am on solid theoretical basis when I have resigned my self to keeping my FC in the 10-15 range. By that I mean CL loss is the same whether FC is 5 and goes to 3 or is at 15 and you go to 13, you still replace 2PPM of CL at the same cost. As long as I never have to SLAM, this works. And I have not had algae before I started BBB and have not had it since.

If you ever want to compare notes on keeping a pool Trouble Free in Tucson, just PM me.
 
One can actually do dilution with DISTILLED or DEIONIZED water to reduce the FC level and measure the pH. This works because the water you are measuring is buffered water so dilution with neutral unbuffered water (i.e. no buffers in it) has a minimal effect on the pH. So you can't use tap water for dilution since that is buffered water.
 
Thank you to all. At least I feel confident enough now to keep monitoring it and allow for the +.3 or so in the reading. Chem geek, I'll try doing some side by side testing with diluted and straight pool water to see if there is a difference. I already use a 1:4 dilution with distilled water on the daily FC OTO test since the color cell only goes to 5, so it won't be hard to check. Wildcat, thanks for the invite. Will definitely take you up on that. Like you, I just hate the thought of water down the drain around here, but there isn't much choice. Could not find any commercial outfits doing RO purification in the Tucson area and it's much pricier than just replacing the water anyway. Will definitely take your advice on draining out a little before a storm (if we ever get one, lol). ;-) Jim H.
 
I think that the pH reads fairly accurately as long as the fc is less than 15% of the cya and the test is read right away. What is your TA?

For dilution, you could remove and add water at the same time such that the water level remains the same.
 
JamesW, TA is 130. That is why I want to reduce pH to 7.2 and aerate. According to PoolMath that is how to adjust the TA down to recommended levels. CH is 625 and don't think I can do anything about that except water replacement, just like the CYA level.
 

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Yes, time to stop the pucks. Immediately. You can save them in a low humidity environment, not a challenge in Tucson, for when you go on a long vacation and cannot use bleach. You do not want to add more CYA that will cause you to have to drain more water. Your are perpetuating the problem the previous wonder started.

Another way I conserve water and reduce my CYA, though slowly, is to clean my cool deck by splashing water from the pool while swimming rather than using a hose to clean sand and bird droppings. A few gallons a day add up
 
jblizzle, As mentioned, I recently got the TF100 kit recommended on the forum. The instructions that came with the kit say that for daily Chlorine and pH tests to use the K-1000 kit that is included with the kit (the blue box with the colored test block). Further, for weekly tests to use the FAS DPD Chlorine test and I have done that. That's how I know my Cl is 13ppm. The reason I dilute the sample is that is the only way to get the color light enough to read in the test block. Where did I go off base? Should I be running all my daily tests with the FAS test? Does my kit sound like it is different than what it should be? I'm confused now.

I'll pull the Trichlor pack and start using bleach right away.
 
The OTO test is not at all precise. With dilution it becomes so imprecise that it is nearly useless. If you really want to know the FC level you should use the FAS-DPD chlorine test. The OTO test is mostly useful for distinguishing chlorine from no chlorine and for getting a general idea if things are more or less alright or have gone terribly wrong. In your current situation, where the FC level is relatively high essentially all of the time, it isn't really very useful.
 
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