Out of whack pool - additional advice appreciated....

[TomU]

I stopped by a friend's house to help him with his pool tonight. The pool is a vinyl IG with a deep end, 24" sand filter, and Hayward 400k heater. He claims it is about 30,000 gallons. The pool is crystal clear. He was concerned about the TA test going from green to light gold (instead of red). Here is what I found:

FC: 23.5
CC: 1.0
pH: < 6.8
TA: 110
CH: 320
CYA: > 120

The first time I checked the FC, I used the 25ml mark and gave up after 120 drops! The color would never totally clear, just go to a light pink. The second time I used the 10ml line and got a distinct transition to clear after 47 drops. I was surprised that adding the 5 drops of R-0003 showed CC. It took two more drops to clear it again. I find it hard to believe that there can be CC with that FC level, even with the CYA as high as it is. Is it possible that the low pH is messing with that part of the chlorine test?

Realizing that we needed to get a handle on the pH first, I used a base demand test to see how far down it was. After adding 30 drops of base demand to the pH color comparator and seeing no change (other than a lightening), I knew we were in trouble.

To attempt to bring the pH up, I added three 8oz whipped cream containers full of pH up (soda ash). I checked it two hours later and could discern no change. I then added about half a pail (guessing 15 - 20 lbs.). I will check it tomorrow morning and see if it moved. I realize that a partial drain and refil is needed because of the CYA level, but I'm really concerned about the heater with this extremly low pH.

FWIW, they appear to have gotten in this situation by using tri-chlor tabs in an inline feeder set on 7 (out of 10). The friend is under instructions to check the TA each day, and adjust accordingly. He has never been told to check the CL, just keep the feeder full. I have turned off the feeder. :-D

Questions I have:
1.) I realize that low pH can affect the chlorine test. Does it affect both the FC and CC, or just one of them?
2.) The low pH seems to make the TA test go from green to gold. Even though its gold instead of red, is the value still accurate?
3.) Does low pH affect the CH or CYA test accuracy?
4.) Since the TA is related to the pH, as I raise the pH, I'm guessing the TA will rise as well. Would it be better to aerate to bring the pH up instead of adding pH Up, washing soda, or borax? I'm thinking this might keep the TA where it is now (which appears to be OK) while still allowing the pH to rise.
5.) With a CYA this high, at what level should the FC be considered unsafe to swim in?

I noticed that the solar cover is falling apart. It has the small triangle shaped "bubbles", and the bottoms of all of them are falling off and floating on the surface of the pool. I'm wondering if the low pH has destroyed them, of this is normal old age. I also noticed after leaving that my hands were very dry. I think this must be a function of the acidity of the water.... :?

Sorry this is so long. Thanks for your advice.

 

[frustratedpoolmom]

I will defer to the experts because much of this is beyond my scopability ; I have some ideas but I don't want to give you incorrect advice.

Is this a TF-100 test kit?

With PH that low, aeration will take too long. So Borax is probably the best choice for raising here. The TA can always be adjusted later.

Others with more expertise will be along shortly to chime in....

 

[TomU]

Is this a TF-100 test kit?

No, Leslie's version of the Taylor K-2006. The TF-100 didn't exist yet when I bought it (neither did this forum ).

With PH that low, aeration will take too long. So Borax is probably the best choice for raising here. The TA can always be adjusted later.

I'm leaning toward washing soda instead just because of the volume of Borax required (double the washing soda). Of course this will affect the TA more... :?

 

[PoolOwnerNumber9]

How are you getting such an accurate free chlorine reading? If it really is 23.5, as you say, then none of your other readings will be accurate. The chlorine will bleach out all of the reagents. The cyanuric acid is also way too high. It has to come down.

 

[dynamictiger]

As mentioned the high chlorine reading may be affecting the testing reagent. However the high cyanuric will affect the TA reading as well as retain the chlorine. I would think if you diluted the sample with fresh water say half pool and half fresh you would get closer to where the water should be. Getting the cyanuric down would be the first step and nothing else should count until that is dealt with.

 

[JasonLion]

You need to get the PH up and CYA level down. Raising PH will be complicated because the PH test is not reliable at high FC levels (tends to read higher than actual).

PH does not have a significant effect on the FC or CC test when using FAS-DPD.

The TA test is still reliable at high FC levels. The colors may change to blue and yellow, or somewhere in between the usual colors and blue/yellow, but the results are still valid.

Low PH does not normally affect the CH or CYA test.

Aeration would be a good idea, but it will be too slow. You don't want the PH down that low and need to raise it fairly quickly. This is compounded by the fact that high FC will cause the PH test to read higher than actual, so the PH is probably very very low.

With CYA that high I would still swim with FC up to about 30. The active chlorine level is far lower than in many indoor public pools. However it is not very good to swim with PH that low.

Washing soda/soda ash will raise the TA level dramatically, which you don't want.

Low PH can damage the solar cover, the vinyl liner, and the heater. Very low PH can cause rapid damage.

 

[Guest]

The TA is actually much lower than tested because with the CYA as high as it is you need to look at the TA contribution from the CYA which is around 30 ppm or higher (since it's impossible to tell just how high the CYA is when it's over 100 ppm. I usually ignore adjusted TA but when the CYa is as high at this pool has you do need to make the adjustment for
CYa.
I suggest the washing soda to get the pH up quickly, then some drains and refilsl to get the CYA down. Once that is done you can worry about rebalancing the water and educating the pool owner.

 

[TomU]

I suggest the washing soda to get the pH up quickly, then some drains and refills to get the CYA down. Once that is done you can worry about rebalancing the water and educating the pool owner.

That is the approach I'm taking. I added almost all the soda ash he had, and will recommend that he begin immediate water replacement. I'm too concerned about the heater to wait to raise the pH by water replacement (even if it does raise the TA).

At what level of active chlorine do the other testing reagants begin to bleach out? As was mentioned, with the CYA as high as it is, the active chlorine isn't nearly as bad as it seems. Are there certain tests that the CYA doesn't help minimize the affect of the chlorine on the testing reagent?

 

[JasonLion]

With Taylor based liquid chemistry, the PH test is by far the most affected (tends to read high) by the FC level and that affect is mostly independent of the CYA level. If you have a DPD chlorine test (shades of pink) it will also be affected by high FC levels (tends to read zero at high FC levels).

With test strips, all of the tests are affected by high FC levels.

Other brands and forms of water testing are affected in various different ways.

The other significant interaction isn't really a test kit based interaction. If you raise PH by any means other than aeration the TA will also go up. Likewise, if you raise TA, the PH will also go up.

 

[TomU]

Update. I re-tested everything tonight. Here is where things are at now:

pH ~7.3 (2 drops of acid demand make it a solid 7.2)
FC 17.0
CC 0.0
TA 230
CH 360
CYA 120 (55 when diluted 50/50 with distilled water)

1.) Is there some scale I can use to adjust the measured pH based on the chlorine level?
2.) Would an electronic pH reader's accuracy be affected by the high chlorine level?
3.) The CH test seems to take a long time to fully change from red to blue. It takes probably 5 or 6 drops to completely eliminate any red hue. Is this normal? Am I correct to continue until no more change is detectable?
4.) If the pool was kept at this CYA level, I'm interpolating that the target FC level should be about 14. Does this seem right?
5.) Regardless of whether or not water is replaced, I'm thinking that now would be a good time to do some aerating. Anyone disagree?
6.) Where is the chart that tells how to adjust the TA based on the CYA level?

Why this happened: Beyond the obvious use of trichlor tabs, it seems like we may have found the root cause. Apparently the timer quit working a couple of weeks back and the pump has been running 24/7 since then. This of course means that there is more chlorine being put in the pool from the inline chlorinator. Apparently this excessive addition of trichlor to the pool is what raised the FC level to what it is now and also lowered the pH. From what I've been told, the pH was on the low side before this started, and the excessive chlorine levels probably masked that the pH had dropped as much as it did. Interpolating from the pool calculator, based on where the pH is now and what was added, I'm guessing that the starting pH yesterday was about 6.7 (assuming the current pH level really is 7.3).

Thanks again!