Why Am I Losing Alkalinity

[Shirker]

6/29
FC 5
CC 0.5
PH 7.5
TA 100
CH -
CYA 20

7/3
FC 2
CC 0
PH 7.5
TA 90
CH 225
CYA 20

7/12
FC 3.5
CC 0
PH 7.5
TA 70
CH 200
CYA 30

Is it normal to lose TA? As you can see in the results above, I have gone from 100 to 70 in just a few weeks. I have back-washed very little and I have not had to add any water (we did get a lot of rain recently. So much that it was above the skimmer). Could the rain water have dropped TA?

Thanks in advance,
Josh

 

[Richard320]

Several things could be at play here.
1) Has pH been rising at all and you've been adding acid?
2) CH has gone down, which indicates dilution. So it would make sense that heavy rains could be the cause.
3) CYA is going up. Are you chlorinating with dichlor powders or trichlor pucks? They are acidic and will lower TA.

 

[Butterfly]

Have you been using MA often to keep pH lowered?

Have you been using trichlor pucks?

 

[Shirker]

Yes, using Trichlor (10# bucket that came with the pool). Plan to stop using the pucks once my CYA is up and/or I run out. PH has been constant with no noticeable changes.

 

[Richard320]

Yes, using Trichlor (10# bucket that came with the pool). Plan to stop using the pucks once my CYA is up and/or I run out. PH has been constant with no noticeable changes.

Mystery solved.

If you look at Effects of Adding Chemicals down near the bottom of poolmath, you can see what using trichlor does to chemistry. Besides adding FC and CYA, it lowers pH. So it lowers pH and swimmers and circulation aerate and pH bounces back up. But the TA goes down. It won't be long now before the TA gets low enough that pH won't bounce back up that fast.

Plug in some numbers. 16 oz (2 pucks) will lower pH by about .4. That's the same as adding 24 ounces of acid. That much acid will also lower TA by about 7.

 

[Shirker]

Thanks, guys!

So using Pool Math, if my target CYA is 40, then I may not be able to use up the whole bucket of trichlor before I need to switch over to bleach. In the meantime, I need to throw in about 6 pounds of baking soda, right?

 

[Richard320]

Thanks, guys!

So using Pool Math, if my target CYA is 40, then I may not be able to use up the whole bucket of trichlor before I need to switch over to bleach. In the meantime, I need to throw in about 6 pounds of baking soda, right?

Why? TA of 70 is acceptable.

 

[Shirker]

I saw that the recommended level is 70-90+, by the "+", I thought it would be better to be on the high end. But if 70 is good for right now, I will just wait and see if it gets any lower before I do anything.

Thanks again for your help. This site is great.

 

[JasonLion]

TA is better on the high end when using trichlor tablets. With trichlor TA at 100 to 120 is good. Once you stop using trichlor there is no point in raising TA above 90.

 

[chem geek]

Since it's a bit of a pain to lower the TA level, you can just add enough baking soda to maintain the ultimate TA level you want. Why don't you start out maintaining 70 ppm and then after you are done with the Trichlor you can see if your pH is stable or not. A lower TA can have less pH rise after you've switched to using bleach or chlorinating liquid.

 

[Shirker]

OK, I will shoot for a 70 until I use up the pucks and see what modifications I have to make then.... Just out of curiosity, when I do switch over to bleach, how often do most of you add chlorine? Do you add it every day and try to keep a perfect FC target? Or do you add it two or three times a week and let the FC drift a little?

Again, thanks for the feedback.

 

[Richard320]

You switch to bleach when your CYA reaches its target.

I think the majority of us start out testing and dosing every day with bleach until the pattern emerges. Then it's dose every day and test every other or something like that. A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

 

[PAGirl]

Everyday is ideal, as you don't want to fall below the minimum. If you can't everyday, then targeting over a bit can keep you from dipping too low.