TF-100 - TA partial red or full red

[austinnichols101]

I'm currently working to get my TA down to 80 to fight a gradual creep in PH. As I get closer to my target number I'm trying to be as accurate as possible with my measurements.

Initially as I add drops of R0009 to the solution I'll see a slight tinge of red which disappears after mixing. As I approach the end of the test there's a point where I'll add a drop which turns the majority if not all of the solution light red. A final drop causes the solution to go to dark red and subsequent drops do not seem to have any significant impact on coloration.

Should I stop counting on the last drop I described (dark red - when the drops have no further effect) or the next-to-the last drop (light red - major color change)?

 

[duraleigh]

Waterbear is the real expert but I'm pretty sure he says to count that last drop that completes the change to red. That is considered the "endpoint" of the test.

 

[JasonLion]

Yes, you count the dark red drop. Another way to put it is to keep adding drops till the color doesn't change any further, and then don't count the final drop which didn't change the color any further.

 

[nitz369]

Just for curiosity, what are you doing to lower your TA level? Mine is at 130 and it would be nice to get it a little lower.

 

[duraleigh]

From JasonLion's sticky:

You can lower TA by lowering the PH to between 7.0 and 7.2 with acid and then aerating the water to bring the PH back up. Aeration can be supplied by spa jets, waterfall, fountain, rain, kids splashing, compressed air, or by aiming a return up towards the surface so it breaks the surface of the water and causes bubbles. This process is then repeated until you reach the desired TA.

 

[austinnichols101]

Essentially I did what Dave described.

First I used poolcalculator.com to determine the amount of acid needed to drop the pH from 7.5 to 7.0. I then went to the bottom of the calculator to look at the 'Effects of adding chemicals' and entered the acid amounts so that I could get a good idea of how far the TA should drop. During this process I also made sure to enter in all of my other numbers so that I could get a good idea of the before/after impact to my CSI.

Next I added the acid in a couple of batches, circulating about an hour between each. I did this so that I didn't accidentally overshoot my 7.0 target (measure twice, cut once). I also started up my aeration because the acid will drop the TA and then the aeration will raise the pH with minimal change to the TA drop. I'm using a PVC fountain that screws on to one of the return inlets. I've found that it takes about 3-4 hours to bring the pH up by .1 with my pool and this specific fountain.

Once I hit 7.0 I ran a test to see what my ACTUAL TA drop was. Now I know generally that if I add 'x' amount of acid I'll drop the TA by 'y'.

Once the pH came back up to 7.2 or so I would add enough acid to drop things back down to 7.0. My goal was to get enough acid into the pool as quickly as possible without dropping things below 7.0. During this process I ran a couple of TA tests just to make sure that I was on-target with my estimates.

Once the TA reached my target of 80, the final final step was to open a beer or two or three and watch the pH rise back to 7.4 - 7.5.

The reason I was targeting 80 was to slow down the pH rise I was seeing as a result of using unstabilized chlorine (via liquidator).