How much acid?

[forkboy]

Hi,

Wondering how frequently I should be expecting to add acid to maintain pH?

About a week and a half ago, I had a reading of 7 after pool guy dumped a bunch of acid in the pool (don't know how much exactly). Yesterday, back up at or over 7.8 (the limit of my test).

I've had to add 1.2L 320g/L (18 baume) HCl to get it back down to near 7.2 - which in itself is confusing as PoolMath suggested 300-400mL @ my TA level.

My TA is ~30, FC 9

Any insight would be appreciated, I am a pool newb.

Thanks
Matt

 

[Texas Splash]

Most commonly, pH increase is attributable to one or more of the following: new plaster curing, elevated TA, aeration. Also keep in mind that unless you have a specific need to pull the pH low (i.e before a SLAM), your pool may naturally prefer a pH in the upper 7s which could be just fine. Your TA is already low (a bit too low), so unless your plaster is new, I suspect the pH rise may be because of the small water feature and/or the SWG. Thoughts?

 

[JasonJoel]

Depends on a number of things such as aeration, plaster age, water temp, as well as TA and borate level.

My pool naturally runs around 7.8. I add acid when it gets above 8.0 and drop it down to about 7.5. I only have to do that about every 2 weeks.

Before I added borates I had to do it every week, sometimes every 3 or 4 days. So needless to say I am a fan of borates.

Note that buffers like borate do not actually reduce your acid needs, you still have to add the same total amount of acid, you just add it in bigger doses less often.

 

[forkboy]

I've been lowering it to initiate a second SLAM for a somewhat persistent algae problem.

Yes, water feature; it is two small waterfalls, that would be aerating quite a bit of water.

Given that, what do I need to look out for? Will I be constantly battling pH and TA levels?

I'll do a bit of research on borates too.

 

[Texas Splash]

Yes, water feature; it is two small waterfalls, that would be aerating quite a bit of water. Given that, what do I need to look out for? Will I be constantly battling pH and TA levels?

I would first recommend getting the TA back up to about 50. A TA close to 30 doesn't help anything at this point. Also consider shutting-off the water features when the pool is not in use. That should help. Since you need to SLAM, go ahead and lower the pH to 7.2. After the SLAM, re-evaluate the chemistry. The pH may rise back to the upper 7s, and if does that should be okay as long as your CH isn't too high. To know for sure, enter your latest numbers into PoolMath and look down at the row titled "CSI". PH has the most impact on that CSI result, but so do TA, CH and water temps. As long as a pH of 7.6-7.8 doesn't create a potential to scale, you should be fine. If you have any other questions about that topic, just let us know.

 

[forkboy]

Many thanks... I will adopt that plan. However;

One thing that's really got me confused though, if my TA level is 30, PoolMath says to go from 7.8 (or even 8.2 since 7.8 is the upper end of my test) to 7.2 should be about 500mL.

Now, pool guy's reading for my TA was 125.

If I use TA 125 in poolmath, it's a lot closer to what I've actually had to add (~ 1.5L).

This makes me question my TA reading, or PoolMath.

Is it possible to test the test kit?