pH properly testing for the correct level

[dolphin]

From reading the Forum here, you cannot accurately measure pH beyond 10 ppm of CL, that much i understand.

In one of the Forums, there are several methods to circumnavigate around the problem.
One of them is by diluting the test sample (1:1 ratio) with distilled (only distilled!) water.

Chemistry wise i'm having a problem understand is:
Methods aside, is it better to get the CL, ideally to "0" zero?
shouldn't there be some CL present as it plays a factor in the level of pH?
If triclor and diclor is in the water, shouldnt the pH be lower since it is acidic by nature? Wouldn't that then bring the pH level higher if the CL level in the test sample for forced to go to zero? Using a strong UV light source for instance?

Of cource the opposite would be true if using Cal Hypo or Sodium Hypoclorite - forcing the test sample to go to zero (0ppm CL) by the same method above, wouldn't that make the test sample appear to be acidic ?

if the test sample where to be brought to 0 ( CL = 0 ppm) is that the correct pH level or is it with some level of the type of CL using that should be included in the test sample but lower than 10 ppm? that is my question

Forcing the CL in the test sample to zero i would use a strong UV light source like a black light etc. or i could use and have been using a microwave oven
with the microwave oven, i'll get it hot but not hot enough to make bubbles

 

[mrcarcrazy]

Diluting the sample with water is a bad idea IMO. The distilled water has a pH...so you will alter the pH of your sample if you add anything to the sample...unless their pH was already identical...which you can't determine.

the best thing to do is accept that pH cannot be accurately measured with a drop test with a FC >10
eliminating the FC by other means sounds a bit like overkill for pool chemistry.

My Question is why is this a problem that you are needing to overcome?

in General, pool owners will get their pH in line before SLAMing the pool. The pH should remain in the tolerable level throughout the SLAM procedure.

 

[jblizzle]

The Taylor pH reagents are designed to handle some FC in the water and still give accurate results. When the FC gets above 10ppm, the chlorine neutralizer is no longer effective and the test will read a false high.

 

[dolphin]

while SLAMMING i get that... ill drop it down to 7 or so on the pH... The pool is fine as far as chlarity and all that but... my CL has to remain high because i do have 50 PPM CYA and it is an outdoor pool in Mexico where the sun is near 0 degree straight up quite strong. Back to the point....

ok so dragging the CL to 0 is overkill so if i just test the sample at 9 or less should be fine then..... no need to compensate for any amount of CL ( below 10ppm ) in the calculation.
right now my CL is at 11 ppm @ 50 CYA so i should expect an ideal pH reading of 7.4 ~ 7.5 if i wait for my sample to drop below 10 ppm of CL ?
7.4 ~ 7.5 is still the ideal pH level with that amount of CL in the water? ( of course my sample will be below 10 ppm)

 

[jblizzle]

You can not wait for the FC in the sample to drop ... because the pH will also be changing in that time.

With a FC of 11ppm, if you quickly read the pH test, it should be pretty accurate ... the color may drift toward pink though which is due to the higher FC levels. The higher above 10ppm you are, the less likely to get a good pH test.

There is no "ideal" pH level that is a function of FC. Assuming you other parameters are in range, just keep the pH in the 7s and you should be fine. IF your CH is higher than recommended, then you may want to keep the pH below 7.5 or so. It really depends on the full set of test results.

 

[dolphin]

oh ok i was just curious because if someone SLAMS a pool.... say with Cal Hypo because of the nature of Cal being 'basic' the TFT forum say to drop pH to very low 7's because adding the CL will raise the pH automatically with the SLAM sized Cal hypo in the water that part i understand.
understandably so, once the SLAM is over and it is time to dramatically lower the CL levels back to its normal levels so would to the pH levels ?? (just out of curiosity).
but from your last thread... i will measure the pH near 10 or as close as possible to CL = 10 to get a good-n-nuff pH reading .
i was just curious as to the chemistry of how CL affects pH, i know all the other chems ( CH,TA n so on) play a role (hence the Langelier formulae somewhat adding all the numbers ends with somewhere around 1 or 1.2 ( i forget now but...) )..

 

[jblizzle]

When you add chlorine (bleach), it does raise the pH; BUT, as the chlorine is consumed, the pH drops also. So, using bleach is effectively pH neutral. We recommend lowering the pH before the SLAM to account for the temporary pH rise when you add a lot of bleach and knowing that pH tends to normally rise anyway in the pool, start the pH low because you may not be able to test the pH for days to weeks while SLAMing.

If you were to use Dichlor or Trichlor to start a SLAM (not typically recommended), since they are very acidic, you would not want to lower the pH first. I though cal-hypo was pretty neutral, but I am not positive off the top of my head.

 

[dolphin]

OMG! no Cal hypo is really basic! but good explanation none the less that while add liquid or cal the pH will rise and then drop back down to the original level once the CL has diminished. And as you say it is an elegant way of saying adding bleach 'is' effectively pH neutral because the pH will rise considerably but drop back down again once the cl level is consumed or is where its level was before adding it in.

my curiosity question is your saying CL is not so much a function to pH ( with the exception to SLAMMING). If my CL on the day to day doesn't really drift too much then the pH vs. CL shouldnt be really a factor. If however, the CL where to bounce from day to day ( normally it would be hard to do) but just for this example it did bounce from 0 to say 20 CL ppm then the pH vs CL would be somewhat significant to factor in? Because it would resemble more and more of a slamming formulae where you now have to take into account all that CL in the water the next day its not ... uuhggh i think i'm just mudding up the water lol no pun intended.
dont get me wrong the water in my pool is fine.. and yes i did slam with great results ... thank you for that ...

 

[jblizzle]

Simply: You want the pH in the 7s, regardless of the FC level. Problem is you can not test the pH when the FC is very high so you try to compensate before raising the FC to the point when you can not test the pH accurately.

According to PoolMath, adding cal-hypo or bleach does not have a direct impact on raising the pH, but we know there is the temporary rise in pH due to the added chlorine.