Why is it so darn hard to get an accurate pH reading?

[bassadict69]

According to my new test kit, my pH has been holding around 7.6-7.8 & I have been steadily adding acid every few days trying to bring it down to around 7.2, but have noticed very little color change on my tester.

Yesterday, I decided to pull 2 water samples & carry them to two different pool stores to get my water tested. All numbers came up about the same as what I come up with using my big test kit...except pH. Yesterday morning I still showed a pH a little higher than 7.6, the first pool store came up with 7.8 (test strips)...the second pool store came up with 7.2 (little cannisters they inject water into then stick the cannister into a reader thing)

Why can't I come up with a definitive pH? Am I using some diluted acid? It is from last year & has been stored in my shed all winter.

Is there a better way of checking pH? Anyone else besides a pool store that can check it & maybe have a more accurate way of doing so?

 

[JasonLion]

Don't trust the test strips.

The standard phenol red PH test included with most test kits is really quite good. The test reagent will eventually go bad, but that normally takes years. The only, at all common, thing that throws the reading off is high FC levels. When FC is above 10 there can be problems with the PH reading higher than it actually is.

If your TA level is high it can take an enormous amount of acid to lower the PH. High TA can also cause the PH to rise fairly quickly, which might give the impression that you were not able to change the PH when in reality it went down from the acid and then up again later. Plaster that is less than one year old will also cause the PH to constantly rise.

 

[bassadict69]

Alk is only at 120...

PH has been checked at several different FC levels...anywhere from 12 down to .5 (oops ) just before shocking the pool. Regardless, it reads about the same! I may try buying another one of the pH drop test kits & trying that.

Pool is vinyl liner AG pool so plaster isn' the problem...

I would get another set of numbers this evening but chlorine levels are being held at 15 right now after my little oops (see above) & letting the chlorine level drop on me...luckily, I think I bumped the Cl levels way up to shock level before the water got TOO bad.

Not sure if it makes a difference, but I have been using both bleach & Cal Hypo shock to quickly raise the levels of chlorine. Does either of these affect pH much?

 

[JasonLion]

How much acid have you been adding? I calculate that it would take about 5 cups of 31% muriatic acid to bring the PH down from 7.6 to 7.2. Not everyone would be able to see the difference one cup of acid made in the PH test.

 

[bassadict69]

By now, probably half a jug!

 

[dschlic1]

I have found that on my pool, that the acid calculators way underestimate the amount of acid need to change my pH. For example in order to lower the pH from 7.6 to 7.3 usually requires at least 32 oz of 31% acid.

 

[JohnT]

I've found that adding 7 drops of the reagent for the pH test makes my test far easier to read. I only use 5 myself, but my interpretation doesn't change between 5 and 7 drops. At 7 drops, the colors are almost identical to those on the test vial. I have the kids put 7 drops in while I'm traveling so I can trust their email reports more.

 

[Guest]

How much acid you need to move the pH will depend on the TA. All the calculators and charts make some assumptions as to this so the BEST plan of attack is to add some acid (good starting point is 1 pt per 10000 gallons) wait about 30 minutes or so and retest pH and repeat this until you get the pH you are looking for. If you have a test kit with an acid demand test you can use that but be aware that this is still an estimate and you still might need to make adjustments to the pH anyway. The best use of an acid demand test is when you need to make a HUGH change in pH. It will get you in the ballpark faster but it won't always get you to the right endpoint.

 

[AnnaK]

I've found that adding 7 drops of the reagent for the pH test makes my test far easier to read. I only use 5 myself, but my interpretation doesn't change between 5 and 7 drops. At 7 drops, the colors are almost identical to those on the test vial. I have the kids put 7 drops in while I'm traveling so I can trust their email reports more.

This is GREAT advice!

I have a hard time with the 7.5 reading. I know it's not 7.2 or 7.8 but to my eyes it could be anywhere in between. Using john's 7 drop method of phenol red lets me know very definitely that it's 7.5. The hue is the same but the saturation is much richer.

Thank you very much for posting this tip, John.

 

[Sharkygirl]

So if I can join in this conversation, how do I calculate an accurate pH with high chlorine then. Since the test is inaccurate above 20ppm of CL for sure. I understand the TA will still be accurate though. So how does one know if they need to adjust? The reason for the high chlorine (43 today) is a long story I will save for another day.

 

[mknauss]

The only reason to have an elevated FC above 10 ppm is for a SLAM. And part of the SLAM process is to lower your pH to 7.2 prior to starting the SLAM.

At the level of FC you state, there is no reliable method using a drop tester to measure pH.

 

[Sharkygirl]

The short story for the long one is I switched pool companies. Went away for the summer (3 MONTHS), When I returned I found pucks in my skimmer for the spa, my Chlorine was 150, TA at 40, pH unreadable, CH 750, Cya well over 100, and greenish tinted water. I replaced over half the water, today I am thinking I will replace half again. I don't know why I just didn't start over because this situation has been driving me mad. (It's been 2 weeks). The pool person said she didn't know I had a SWG system!!!! Furthermore, there were pucks in the pool in a floater as well. I was livid to say the least. So today I'm still at 43 for a CL reading. My TA is 110- I raised it too high, learned my lesson. The pH reads 7.6, but I believe it may be lower. CH is now 550. Salt is 3400. This pool person clearly doesn't know pools. She apparently has been doing pools for decades, but for her to not know I have a SWG is pretty scary. This is my 3rd pool company in 5 years, so I am going to try and educate her on my pool system and hopefully over time she will be able to handle things for the 3 months a year I'm away.

 

[jliddil]

Get pH meter. They are cheap on Amazon.

 

[tomfrh]

I've tried strips, store tests, electronic meters, and good old Phenol Red.

I would never use anything but Phenol Red. After a while it's very easy to read. I can now easily eyeball when it exceeds 7.8, which is the threshold i use. There's a certain magenta hue that appears that is easy to pick.

As for dropping pH to 7.2 - I don't see the need. You end up chasing your tail. I used to do that, but now drop to 7.6-7.7 and add cup of acid when it exceeds 7.8





When my FC has been high (e.g. above 10) I've mixed up 50:50 with tap water to measure it. E.g. If tap water is 7.4 and 50:50 mixture is 7.5 your pool water is close enough to 7.6

 

[mknauss]

If you are reading a TA then your pH is not crazy low. I would suggest adding baking soda to raise TA to 70 and once the FC drops into lower teens test ph again.

That was not a pool service. They were a destroyer.

 

[Sharkygirl]

The short story for the long one is I switched pool companies. Went away for the summer (3 MONTHS), When I returned I found pucks in my skimmer for the spa, my Chlorine was 150, TA at 40, pH unreadable, CH 750, Cya well over 100, and greenish tinted water. I replaced over half the water, today I am thinking I will replace half again. I don't know why I just didn't start over because this situation has been driving me mad. (It's been 2 weeks). The pool person said she didn't know I had a SWG system!!!! Furthermore, there were pucks in the pool in a floater as well. I was livid to say the least. So today I'm still at 43 for a CL reading. My TA is 110- I raised it too high, learned my lesson. The pH reads 7.6, but I believe it may be lower. CH is now 550. Salt is 3400. This pool person clearly doesn't know pools. She apparently has been doing pools for decades, but for her to not know I have a SWG is pretty scary. This is my 3rd pool company in 5 years, so I am going to try and educate her on my pool system and hopefully over time she will be able to handle things for the 3 months a year I'm away.

okay, update here. I dumped another 1/2 of my spa water, (this is the second time). Last night things were perfect except for my CA being a little on the low side at 225. Understand my hot tub is 600 gal concrete, outside in the hot weather, never covered, I have an autofill, SWG, DE Filter, and heater. So it is basically a small pool. Has it's own equipment. I had the TA at 60 last night, but I wanted to get the CH up just a little. I was shooting for 350 and overshot a little. Today it is at 425. Consequently I raised my TA to 90. Higher than I wanted, but okay. So here is the mystery. Last night my Chlorine was 8.5. My husband and I were finally able to sit in the hot tub and relax after my two week stint of trying to get the water under control again. This morning, my CL was at 14! What??? I have the chlorinator turned to 0% because I wanted to see hot far the chlorine would drop overnight. It does not make sense the CL would go up! No CC's, I checked that. So I went to check the chlorine again this afternoon at 2pm, it went up to 16!! What the heck is going on? I did not add anything else other than some salt and the Calcium Chloride flakes. Also, last night my CYA was perfect at 60. Today it is at 80. How can this be??? I have one iAqualink board, two separate bodies of water and one set of equipment for each. All I can think of is maybe there is some residual stuff in the DE filter? or Could the wires be crossed between the pool and the spa? Meaning if the pool SWGs at 30% and the Spa is at 0%, is it possible it is reversed? Any ideas anyone?

 

[santacruzpool]

Any pucks still somewhere (skimmer, feeder)? What about some sort of water exchange with the big pool?

 

[Sharkygirl]

Any pucks still somewhere (skimmer, feeder)? What about some sort of water exchange with the big pool?

No pucks in the strainer, no water exchange with the big pool, they are both separate bodies of water. The Chlorine has to be coming from somewhere. Usually people struggle with not enough. I have too much. It isn't posslbe that the SWG would be making chlorine when it's set to zero, is it?

 

[santacruzpool]

I guess anything is possible, but there is usually a solid explanation once things are broken down step by step. The most important question I have is what test kit, or method, are you using to test your water?

What are the actual models of your 2 Jandy Aquapure SWG's?
What is the Chlorine Level in the big pool?
Is the chlorine staying steady in the big pool (so you can tell if the right Aquapure is in fact feeding it chlorine)?
Any bubbles coming out of the pool, or the spa, while it is running (to tell if the SWG is running in one or the other)?

 

[Sharkygirl]

I guess anything is possible, but there is usually a solid explanation once things are broken down step by step. The most important question I have is what test kit, or method, are you using to test your water?

What are the actual models of your 2 Jandy Aquapure SWG's?
What is the Chlorine Level in the big pool?
Is the chlorine staying steady in the big pool (so you can tell if the right Aquapure is in fact feeding it chlorine)?
Any bubbles coming out of the pool, or the spa, while it is running (to tell if the SWG is running in one or the other)?

TF100 Test Kit

SWG is Jandy Pro Series Aquapure Electronic Salt Water Chlorinator Model#H0263500C for the pool board and PurLink Water Purification System Power Center and Cell Kit for the Spa Board

Chlorine in the big pool is at 8.5 with a TA of 90 - My pool is not in the full infinity edge mode right now because I am having some deck and glass work done at an edge of the pool. So I only have it circulating in the main body of water and not the infinity edge trough. This is making me babysit it at the moment because normally I have to adjust my TA/pH to make up for the pH rise from the constant water motion over the edge. But right now it is running like a normal pool. I drained some of the water and have the autofill turned off so the work could get done-- tile can't get wet right now. The salt is getting a little more concentrated in the pool from the water evaporation, so I haven't been relying on the SWG for the pool, rather just adding bleach and adjusting pH as needed. (My salt is reading 4.6, too high, so I was thinking it probably isn't making chlorine for the pool anyway- When I add the water back in after my tile work is done, that salt will dilute out okay I'm thinking.) Sorry for that long answer. The SWG for the pool is at 35% just in case it is working. I am not getting the warning light or code.

I don't understand the bubble question, when the spa pump runs, it's jets are running, so bubbles yes. For the pool, I never have bubbles.

So to add to the mystery, I may be getting somewhere. I turned off the SWG for the pool completely at 2:15pm. I checked my levels again in both the pool and spa. The spa went from CL of 18 at 2pm down to 13 at 4:10pm. So I am thinking I might be right about the wires crossed in the main board perhaps. You see I just got a new board installed in the last couple of months when I was away. Since I was away I was relying on the pool company to make sure things were working properly. When I got home a couple of weeks ago is when I found the wacko levels in the spa. See above posts. So I am going to check the levels tonight again around 11pm and see where they are. If they continue to fall, as has just happened when I turned off the SWG for the pool, then tomorrow I will turn on the SWG for just the pool again and see what happens to the Chlorine in the spa. If the CL starts to go up again in the spa, my crossed wires must be the answer. Do you agree?