Test Kit for pH - How to distinguish higher pH levels

[bobandsherry]

The shades of red at the upper scale don't seem to be easy to distinguish in Taylor test kit for pH, and readings don't show anything above 8.0. My pool seems to naturally want to level out on the higher end (due to recent build/plaster and SWG). Trying to keep lower just ends up a fight in futility in adding muriatic acid every other day. Based on suggestions from those here, I've adjusted my pH target to be 7.8 and tweaked the other goals accordingly to get to a slightly negative CSI.

With the test kit I don't see much difference in 7.8 vs 8.0, and since the test tops out at 8.0 there's no what to know how high your pH may be. I find that adding a drop of Acid Demand (R-0005) the colors are much easier to discern the readings (oranges and yellows). What I'm trying to understand/confirm is how much each drop of Acid Demand lowers the reading. From informal testing it seems that each drop is roughly ~0.2 change. From my current pool test, it looks like my pH is currently between 7.8 and 8.0. If I add 2 drops of Acid Demand the reading is somewhere 7.4-7.6. Is the assumption of ~0.2 change for each drop correct? Or conversely, how can I determine what my pH level is when it tests at the higher range.

FYI, here's my latest tests results, my current targets are in brackets on the right:

Water Temp - 72F

FC: 4.6 (4.0)
CC: 0.0 (0.0)
pH: 7.9 (7.8)
TA: 70 (60)
CH: 300 (300)
CYA: 50 (55)
Salt: 3300 (3000)
CSI: -0.08 (-0.27)

 

[pooldv]

You are on the right track. TA as low as 50 will be fine. Mine pH is better with TA more toward 50. I'm not familiar with the acid demand test. This PH test reads up to 8.2.
TFTestkits.net K-1000
Also, holding the test up to a bright sky or in front of a white plate or something helps too.

 

[JoyfulNoise]

Your assumptions only work for a given TA level. The amount of pH change per droplet of acid demand reagent is related to not only the concentration of the acid in the drops but also what buffers (carbonates, borates, cyanurates, etc) are present in your water, i.e., TA. If you want to do what you are describing, then you'll need to use chem geek's (Richard Falk) spreadsheet to do the calculations. See this post - Question about Taylor K-2006 kit and pH testing

Be warned, his spreadsheet is not for the faint-of-heart....

 

[bobandsherry]

Thanks JoyfulNoise, that thread is exactly what I was looking for. Spreadsheet is not too bad except to decipher exactly what section determines acid demand droplet change However I don't have the readings for the other buffers (carbonates, borates, cyanurates, etc) so probably not going to help. But information is useful, thanks for pointing me to the thread.

 

[needsajet]

The acid demand drops do not represent a specific change in pH for the reasons Matt explained.

In your example, 2 drops achieves a pH of 7.5 in your test sample. You can then use the table in the instruction book to see how much acid to add for your size of pool to achieve 7.5 pH.

If you had high TA, you would find that 2 drops drops the pH less. If you had lower TA, you would find that 2 drops will reduce the pH more.

 

[bobandsherry]

Thanks needsajet - understand that as pH is lower the change is different. Until my plaster has fully cured I'm setting my target on the higher side for now (with tweaks to other levels to keep CSI level in check) as 7.4-7.6 is vaporized in a day of adding MA, seems to level of around 7.8-8.0 for now. So my interested was only on how to distinguish at the 7.8 - 8.0 as I don't want to be at 8.0 or above, however the Taylor kit maxes out at 8.0 and color variance in 7.8 and 8.0 isn't that much different to see the real difference. Or perhaps there's a better way to verify visibly for these higher levels.

 

[needsajet]

My situation is very similar over the past year, so I like to let the pool ride at pH 7.8 as long as I can. And that's for sure, I have the exact same problem seeing what's happening around 7.8/8.0.

I used the acid demand drops to help me with that. It will be different for different pools, but I found that if 1 drop only reduced the sample pH to 7.7/7.8 then it was time to add acid. If 1 drop reduced the sample to around 7.6, I could hold off until my next test (I usually test 2-3 times per week). Of course your situation will be your own, but you may find that the drops help give you confidence that the pH isn't getting too far out of line.

 

[needsajet]

I should have mentioned that as soon as you see it darker than 7.8, it's time to add acid. You can try adding fairly small amounts of MA, because you'll also notice that your pH rises slowest when it's up near the top of the correct range. You'll use the least acid this way, but in my case, I had to stop worrying about TA because the smaller additions just left my TA pretty much where it was.

 

[bobandsherry]

My situation is very similar over the past year, so I like to let the pool ride at pH 7.8 as long as I can. And that's for sure, I have the exact same problem seeing what's happening around 7.8/8.0.

I used the acid demand drops to help me with that. It will be different for different pools, but I found that if 1 drop only reduced the sample pH to 7.7/7.8 then it was time to add acid. If 1 drop reduced the sample to around 7.6, I could hold off until my next test (I usually test 2-3 times per week). Of course your situation will be your own, but you may find that the drops help give you confidence that the pH isn't getting too far out of line.

That's pretty much how I've been approaching my readings. I'm tweaking my pool chem a bit as I'll be gone for 2 weeks on vacation and wanting to get the pH to stabilize. Adding one drop of Acid Demand was dropping the pH test to 7.6 so I thought I was on the reasonable track of understanding. The changes seem to be helping, and also with cooler temps, but wanted to get confirmation on how to interpret the readings that were in the darker red (7.8/8.0) range. With my current results a pH of 8.2 still shows CSI as balanced so I hope that I'll be good my 2 week vacation without worry of the pool water getting out of control.

 

[pooldv]

Yes, balanced CSI is more important than a raw pH number. There have been a few folks who let their pH run above 8.0 and it seems to be ok. In any case you will be fine for 2 weeks even if your CSI doesn't stay balanced. It takes longer than that for real problems to develop with scale.

 

[xyz]

If you are tracking your acid use, you coul add up a weeks worth, then add 1/7th of that per day. Then adjust that amount is small increments as your PH stabilizes. Then you could reduce the number of times you need to measure per week.