Confused with discrepancy...

[steveinaz]

The Taylor test kit table on acid demand calls for 11.92oz of Muratic, when 1 drop of acid demand agent is needed to get to desired pH. The pool calculator however, says 4.3oz for the same result; ie going from 8.0 to 7.8. That is quite a difference. Is this due to the calculator also accounting for TA?

 

[JamesW]

The pool calculator does not have an input for acid demand results.

An acid demand test uses actual acid on the sample, so the results are experimental vs theoretical for pool math.

Poolmath gives a good estimation for pH changes.

 

[steveinaz]

For example; using the Taylor kit if I want to go from 8.0 to 7.8 pH, the acid demand test requires 1 drop. The booklet chart then says for 1 drop required to get to my target, in my 13k pool, 11.92oz of muriatc is required.

Now, when I put in the calculator that I measured 8.0 but have a Target of 7.8 it tells me to use 4.3oz of Muriatic.

So which is it? 11.92 oz or 4.3oz?

 

[Jimrahbe]

Steve,

I entered the data into a different pool program and found that to go from 8 to 7.8 takes 4.8 oz with a TA of 70 and about 12 oz with a TA of 200

I suggest that you use the pool math number and see what happens.. Worst case, you will just have to dose again, but I doubt it..

Thanks,

Jim R.

 

[JamesW]

Maybe you're not reading the pH correctly.

 

[steveinaz]

That's my observation---I believe the pool calculator is taking TA into account---where as the Taylor table just simply relies on gallonage and # of drops of acid demand test. So I would imagine the pool calculator is the way to go.

 

[JamesW]

In your other post, you're saying that the pH is 7.8. So, there's no reason to add acid.

In my opinion, you seem to be overeager to add acid.

The acid demand takes the TA into account because it's measuring actual results from adding acid.

 

[cfherrman]

Acid demand is your water with acid, it's like a simulated result.

Your pH test will cap out at 8 so you can be over 8 and pool math cannot account for that.

I use acid demand and some math to see where my ph is really at by dropping it to 7.6 (I think) with the demand test and the 7.8-7.6 color shades are much different (I think) so I can tell if the pH is 7.8 8.0 8.2 etc.

 

[steveinaz]

The purple colors of the higher pH values get a little more difficult to distinguish.

 

[cfherrman]

It's good that you can keep it to the +/- one drop accuracy, it still is a very inaccurate way to do tests and I promise you, you will have testing error soon or later, and while your trying to get your dial set on the swg you fo not even want a chance of testing error

 

[steveinaz]

In your other post, you're saying that the pH is 7.8. So, there's no reason to add acid.

In my opinion, you seem to be overeager to add acid.

The acid demand takes the TA into account because it's measuring actual results from adding acid.

Actually I'm trying to do the opposite. I'm NOT eager to add acid, but I have been using the Taylor table which calls for 11.9oz of acid----however, the pool calculator is saying only use 4.3oz; so in an effort to reduce acid use, I'm trying to figure out why there is such a difference in dosage between the 2 to get the same pH drop. If I follow my Taylor test results and dosing, my pH has been managed perfectly in the past; YET my TA is lower than it has ever been. For my last 2 pools, in this same township, same water supplier, same Taylor test kit, TA was always been apprx 120ppm consistently in both pools. Now I'm at 50 and trying to understand why.

 

[JamesW]

I think that you're using a pH target that is too low and I suspect that you're probably reading the pH as higher than it actually is.

It's important to manage the CSI so that the water is not excessively aggressive to the plaster.

 

[steveinaz]

My target is 7.8 now...I was using 7.6 in the past. I haven't added any acid in 11 days now. I'm not new at this. This is pool #3, and have used the BBB method and Taylor test kits for over 12 years.

Can you explain to me why the Taylor chart is telling me to add 11.9oz (13k gallon pool) of Muriatic acid for 1 drop of acid demand drop to get to my target (8.0 to 7.8), BUT the pool calculator is saying to only add 4.3oz of Muriatic acid to go from 8.0 to 7.8? This has been my core question from my first post.

 

[JamesW]

When you're doing the acid demand test, I suspect that you are not reading the pH correctly.

So, the acid demand test won't be accurate.

 

[JamesW]

Note that the pool calculator is just an estimate. It should be reasonably accurate for most situations.

There are two sections that calculate pH change in the pool calculator.

The pH change section and the "Effects of adding chemicals" section at the bottom of the pool calculator page give two different results for amount of acid and pH change.

Maybe the calculations could use some updating?

 

[chiefwej]

I generally find it easier to read my pH tests by using 4 drops of reagent instead of 5.

 

[cfherrman]

Acid demand your pH lower to the easier shades, then use pool math and the Taylor charts to see where your starting pH should gave been.

Since acid demand uses your water it is more accurate than pool math as pool math can have inaccuracies in it from test error

 

[steveinaz]

So, did some tweaking--bumped up TA a bit, and allowed pH to level at 7.8. Today's measurements:
FC=4
CC=0
pH=7.8
TA=60 (upped from 50)
CYA=70
CH=820
SA=3800
CSI= -.06
Temp=61degrees

Next weekend the pool will be much warmer, and I'll put the IC40 SWCG back in system. I'm going to use Taylor's recommendations on acid demand.