PH Testing

[Vincent Fontenot]

Good Afternoon
I have a Taylor K-2005C Test kit. I'm pretty good at all my tests but am horrible sometimes at my colors..especially between 7.6 and 7.8 on the tester. When I test the water it looks like 7.8 and 7.6 to me. So. I thought if I add a drop of T-0005 Acid Demand Reagent, it should give me an idea where I'm at. Added 1 drop and the color went to 7.4..added 2 drops 7.2. So my question is if I add a drop of acid demand and it goes down to 7.4 wouldn't the start off PH be 7.6 and not 7.8?

 

[JoyfulNoise]

The drop in pH with acid demand drops depends on what your starting TA is. The booklet that comes with the Taylor kit and contains charts for relating acid demand drop count to acid additions assumes that your TA is within their specified ranges. That may or may not be true if you are following TFP.

The acid demand drops correspond to approximately 9.2 fluid ounces of full strength MA added to 10,000 gallons of pool water. In order to know where your starting pH was, you need to use PoolMath with your current TA, CYA and Borate values and then scale up the amount of acid added. So one drop of R-0005 corresponds to (10,000/17,250) * 9.2 = 5.3 oz of MA. If you use that number in PoolMath, you can see if your starting pH and ending pH match to what you think it is.

But, there's a problem...of course. The acid demand drops are very course and correspond to a lot of acid added all at once. This means that one drop of acid demand reagent will probably correspond to a pH drop of 0.2 units or more. So getting a precise back-tracking of where your pH started off at is really not easily accomplished. In other words, the errors involved here are very big so you really can't say for certain that you were exactly at "this" pH value or "that" one.

My suggestion would be if you really are having a hard time and you've exhausted all methods of lighting and backgrounds to get a good color distinction, then get a cheap(ish) digital pH meter and use both the drops and the meter for a while until you feel like you can tell the colors apart. As long as you get a halfway decent meter and keep it properly calibrated and stored, it can last a year or more and give you plenty of time to "train" your color perception skills.

 

[Vincent Fontenot]

Thank you!