pH base demand testing

[lka674]

Can anyone advise me on how many units of change is represented by 1 drop of pH base reagent?

I'm using it to get a better pH calculation and it took me 4 drops to get down to around 7.0 where the color matched....adding back does this give me 7.4 or 7.6 or 7.8? :?

Many thanks!

 

[chem geek]

The answer depends mostly on your TA level. However, it usually takes a lot more [EDIT] acid [END-EDIT] (so drops) to go from 7.2 to 7.0 than it does to go from 7.4 to 7.2. I would guess that your pH is probably closer to 7.4 and isn't higher than that. However, instead of using the drops, just use a different amount of pH indicator reagent to get the saturation to match your standard and then match based on hue more than anything else. See this post for a couple of rough guides to colors at the different pH levels when using a phenol red indicator.

[EDIT] HOWEVER, if you were adding base demand reagent, then your pH is BELOW 7.0 and you need to add base to raise the pH. See James's post below for the amounts represented by the acid and base demand reagents. [END-EDIT]

 

[JamesW]

If you're using the Taylor Acid Demand reagent to see how much acid it would take to lower the pH to a certain point, one drop of Acid Demand reagent is equivalent to 9.16 fl. oz. of 31.45 % muriatic acid added to 10,000 gallons.

For your 12,000 gallon pool, 4 drops of acid demand correlates to 44 oz of muriatic acid.

You can use the pool calculator to get an idea of how much that amount of acid would lower the pH. The pH section will be more accurate than the "Effects of adding Chemicals" section.

For example, if you had a TA of 110 ppm and a Borate level of 50 ppm, then going from a pH of 7.4 to a pH of 7.0 would take 45 fluid oz of muriatic and would about equal to 4 drops of acid demand.

However, if your TA were 60, then 4 drops of acid demand would correspond to a starting pH of closer to 7.6.

If you're using the Taylor Base Demand reagent to see how much Sodium carbonate it would take to raise the pH to a certain point, one drop of Base Demand reagent is equivalent to 5.13 oz. (weight) of sodium carbonate added to 10,000 gallons.

For your 12,000 gallon pool, 4 drops of base demand correlates to 24.6 oz weight of sodium carbonate.

You can use the pool calculator to get an idea of how much that amount of base would raise the pH. The pH section will be more accurate than the "Effects of adding Chemicals" section.

Note: The acid demand reagent lowers the sample pH, and the base demand reagent raises the sample pH.

Also, most people can match the pH color within the range of the color chart. Using an acid or base demand reagent will probably not be worthwhile, or helpful. It will probably make things unnecessarily complicated.

You might want to get a second opinion from another person if you are having trouble discerning the color. However, it's important to match the color immediately as the pH can drift if the sample is left too long.

 

[lka674]

FC = 5.5
CC = 0
TC = 5.5
pH = ??????
TA = 60
CH = 430
CYA = 50
Bor = 50

Here's my dilemma....STILL....I have one of those digital pH meters and when I use it in the pool I get a reading of 7.4....I calibrate before each reading to a 7.0 calibrating solution, test the pool, then go back and test the calibrating solution to make sure that it is still reading correctly.

However...when I use the drops (and I've bought 3 new bottles from different stores thinking my R-0014 was bad).....the 9ml comparator is showing PINK....not orange casted (indicative of 7.4ish)....but PINK....not 7.8ish...but definitely somewhere between 7.6 and 7.8. I can't even see an orange cast, so I'm really confused. I also have 2 different comparators from 2 different kits.

If I start dropping base to get it up to a color I can recognize...it takes me about 4 drops to get it from this weird pink color to truly 7.8. I'm trying to determine if I subtract those drops unit for unit for ppm if that means 7.8-4 drops= pH of 7.4.....which does match my meter. I just don't understand why I can't see ANY orange at all to start with.

I know I'm likely getting WAY too obsessed with the testing, but I need to know what to trust (my digital meter or my drops) because it's important for me to keep the pH in a certain range to keep my CSI below 0 due to my CH. I WANT to trust my drops....but it's making me crazy that there is zero orange hues. Clearly, I am a type A perfectionist...I WANT to see orange...why don't I???!!!

 

[chem geek]

What happens if you add one drop of R-0007 thiosulfate chlorine neutralizer to your sample, mix, and then do your pH tests (both with the meter and then again with the drops)? Though neutralizing chlorine in this way can change the pH, it would be interesting to see if not having chlorine in the sample makes the two readings match better. You could also try adding one drop of 3% hydrogen peroxide as a separate experiment. If in all cases your pH meter is reading lower than the color from the drops, then I'd question the accuracy of your pH meter. You could also get R-0004 drops as another point of comparison, though that's designed for a larger 44 ml sample size.

 

[lka674]

Thanks Chem Geek....it's the darn meter! So it goes.....another $80 down the drain! LOL
I did do your suggested tests however, and the meter was still way off...even worse than before, so I circle filed it! ;-)