Reducing TA (so that I can eventually add borates)

[werd98]

I've had a hard time lowering my TA (which I want to do so I can add borates). I've added about 75% of the muriatic acid that the PoolCalculator.com recommended to go from 7.6 to 7.2, but it looks like I only got the pH down a bit, and the TA didn't budge. Here are my readings:

FC 1.5
CC .25 (it was just slightly pink, and a whole drop seemed overkill)
CYA 5 (after almost 3 lbs of CYA, I finally got some cloudiness in the test tube, yay! but it was still easy to see the dot. Inching upwards!)
pH 7.5
TA 230
CH 160

It seems that I need to bring the pH down way farther before it'll start dropping the TA, to between 6.8-7? Is it safe to swim in such low pH's? If not, how long does it take to come back up?

 

[jblizzle]

What is the TA of your top off water? Borates may not be a good fit for you.

 

[Charlie_R]

If your top-off water TA is significantly lower than your pool water, and you don't have pets or wildlife that drink from your pool, you can lower your TA.

Best not to go below 7.2 on the pH, and use aeration to bring the pH back up. For this, point a return ball toward the surface so the water ripples, or create a shower type fountain to speed the process along.

Keep an eye on the pH and lower it when it gets close to 8.0. Repeat as needed to reach your target.

 

[chem geek]

It's faster if you add acid when you see the pH rise say from 7.2 to 7.4. The rate of carbon dioxide outgassing slows down as the pH rises so waiting until it gets to 8 could be very slow especially as the TA gets lower. See this table to get an idea of how over-carbonated a pool is at various pH and TA levels.

 

[werd98]

Quick question: why do you need to lower TA when using borates? And related, how high can my top-off water be, while deciding whether to go with borates? Thanks!

 

[duraleigh]

FC 1.5

Off topic but that number jumps off the page to me. You need to keep chlorine in your pool.

 

[werd98]

FC 1.5

Off topic but that number jumps off the page to me. You need to keep chlorine in your pool.

Thanks for the note, however I am concerned with putting too much FC until I get my CYA to the target of 20-30. In looking at chlorine-cya-chart-t2346.html (I've added CYA 5):

CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd Min ...... Shock FC ..... Yel/MstrdShock
0 ................. 0.071 ........... 0.111 ................ 0.151 .................. 0.641 .............. 1.501
5 ................. 0.375 ........... 0.575 ................ 0.75 .................. 2.0 .............. 3.0
10 ............... 0.81 ............. 1.21 .................. 1.61 .................... 4.5 .................. 7.1

... it seems that for a CYA of 5-10, I should be around 1.5ish? I did see the footnote saying that FC of 2 is a realistic minimum, so I did put some more 10% bleach in this morning, which should bring me up to at least FC 2. I really hope my CYA comes up to something reasonable soon - waiting a week to measure after adding it is hard!

 

[duraleigh]

I understand now. Generally, we say that once you dose CYA to a certain level, it's OK to assume that much is in there even though it may not have shown up on the test.

If you dosed to get 30 (or whatever) CYA, I would chlorinate as if it existed in the pool.

 

[chem geek]

Quick question: why do you need to lower TA when using borates?

It's not essential, but makes things easier. The reason is that the TA lowering process works by lowering the pH and keeping it low while aerating the water. If you don't have borates in the water then it takes less acid to get the pH low initially and you can see how the pH rises as an indication of your progress and then add more acid. Finally, and most important, is that at the end of the process you want to raise your pH by aeration alone and when the TA is lower without borates this is still possible in a reasonable amount of time.

With borates, it takes a lot more to make the pH move. So it would take more acid to lower the pH initially for the TA lowering process and then aeration won't have the pH rise very much which is OK and in some ways more efficient but it can seem like nothing is happening unless you were to test the TA. Even worse is at the end of the process where you want to aerate to raise the pH -- that will take a lot more aeration so a lot longer to occur when borates are present.

 

[jblizzle]

The major reason to add borates (at least in my mind) is to slow the pH rise due to SWG or a lot of aeration. There are other reasons that are more subjective (feels better, looks better, etc).

When the TA is high, that in and of itself will tend to make the pH rise. If you add borates when the TA is high, it is still going to try to pull the pH up and then will require more acid to lower the pH back down because you now have borates buffer it.

Thus, you want your TA low before adding borates, so that hopefully the pH will be stabile. But if the only reason you are looking add the borates are the secondary subjective aspects, maybe the pH rise does not matter to you.