I have a pool with way-too-high CYA (175 ppm), an issue inherited from the prior owner of my new house/pool. I am planning to do a drain/refill in the near future to correct this issue.
In the meantime, I am running with intentionally high FC, between 15 and 17 ppm to counter the effect of high CYA.
I've been running like this for about a month now, making regular chlorine additions to hold levels steady, but I'm handcuffed when it comes to maintaining proper pH. I know that my Taylor pH test is likely to give false high readings when FC is above 10. So, after much reading in the forum here, I've tried using a 50/50 dilution with distilled water for the test, and even neutralizing undiluted pool water with a drop of Taylor thiosulfate reagent.
Here's a rundown of results using these three approaches a couple of days ago:
Undiluted pool water: pH = 7.6 (likely wrong due to interference from high FC - I seem to get this result EVERY time I test with undiluted water)
50/50 pool water/distilled: pH = 7.6 (again, likely wrong)
Undiluted pool water, 1 drop thiosulfate reagent: pH > 8
I am pretty sure my pH is quite high, as I've added very little acid to the pool since taking over about a month back.
So finally, my question: Is the Taylor ACID DEMAND test still valid when used with high FC (15 - 17 ppm) water?
With an undiluted sample that reads (false) 7.6, I added the acid demand reagent and found I needed 2 drops to hit a target pH of 7.5 and 3 drops to hit 7.4. That would suggest an addition of 20 to 30 fluid ounces of muriatic acid for my pool.
BUT - I don't know if these numbers are valid given my high FC level. Using PoolMath "backwards" I can determine that if I really needed to add 20 oz of acid to hit 7.5, then my actual pH must be 8.2 - this can be done by trial and error by changing the current pH value until the required acid addition is 20 oz.
So - can I believe the acid demand test, even though I think the pH reading of 7.6 is wrong due to high FC?
In the meantime, I am running with intentionally high FC, between 15 and 17 ppm to counter the effect of high CYA.
I've been running like this for about a month now, making regular chlorine additions to hold levels steady, but I'm handcuffed when it comes to maintaining proper pH. I know that my Taylor pH test is likely to give false high readings when FC is above 10. So, after much reading in the forum here, I've tried using a 50/50 dilution with distilled water for the test, and even neutralizing undiluted pool water with a drop of Taylor thiosulfate reagent.
Here's a rundown of results using these three approaches a couple of days ago:
Undiluted pool water: pH = 7.6 (likely wrong due to interference from high FC - I seem to get this result EVERY time I test with undiluted water)
50/50 pool water/distilled: pH = 7.6 (again, likely wrong)
Undiluted pool water, 1 drop thiosulfate reagent: pH > 8
I am pretty sure my pH is quite high, as I've added very little acid to the pool since taking over about a month back.
So finally, my question: Is the Taylor ACID DEMAND test still valid when used with high FC (15 - 17 ppm) water?
With an undiluted sample that reads (false) 7.6, I added the acid demand reagent and found I needed 2 drops to hit a target pH of 7.5 and 3 drops to hit 7.4. That would suggest an addition of 20 to 30 fluid ounces of muriatic acid for my pool.
BUT - I don't know if these numbers are valid given my high FC level. Using PoolMath "backwards" I can determine that if I really needed to add 20 oz of acid to hit 7.5, then my actual pH must be 8.2 - this can be done by trial and error by changing the current pH value until the required acid addition is 20 oz.
So - can I believe the acid demand test, even though I think the pH reading of 7.6 is wrong due to high FC?