Low TA OK??

[dawndenise]

I've detailed my TA/pH cycle here: http://www.poolforum.com/pf2/showthread.php?t=6983 - second post. Mostly, I'm trying to keep my TA at 80 and my pH at 7.5-7.8.

Yesterday's numbers:

pH 7.5+
TA 60

FC 13.0 (coming down from a shock)
CC 0
CH 250
CYA 45-50
Salt 3600
Water temp 75

This is the time I'd normally add baking soda in 2 doses over 2 days to raise my TA to 80. But when I do, my pH slides right on up to 7.8 or higher, necessitating acid which drops my TA again.

With the full picture, does it still seem OK to let my TA settle in at 60?

I have a waterfall that's on 8 hours/day, same as pump time right now. SWCG is at 40%. Borates are not an option for me at this time.

Thanks for any opinions.

[chem geek]

If you want to keep your TA at 60, you will need to do two things to be in better calcium carbonate saturation (assuming your pool is plaster/gunite, not vinyl). You need to get your CH higher to at least 400 ppm (500 ppm is OK as well) and you need to have your target pH be closer to 7.7 instead of 7.5.

Every pool is different and your higher CYA level and your higher salt level make your pool requirements for a lower TA different than other pools. Normally for SWG pools, especially those with the CYA in the 70-80 range, we don't go lower than about 80 in TA. But it's really just calcium carbonate balance so with higher CH and target pH one can go quite low in TA.

The only thing to remember is that with the lower TA you should be very careful about using acidic chemicals in your pool such as switching to Trichlor for chlorine or adding non-chlorine shock (which is acidic). The pH shifts won't be huge, but they will be larger than they otherwise would have been.

You might try out the lower TA briefly before increasing the CH (but do use a target pH of 7.7) because if it doesn't help you then there's no point in doing it and increasing your CH (since it's hard to reduce once you've increased it -- drain/refill is the main way to reduce it).

Richard

[dawndenise]

Richard, thanks for the info. Yes, I have a gunite pool. I may try out a test week or two with the lower TA and see what happens to pH before thinking of increasing CH.

As the season progresses, I had planned on even increasing my CYA level to a solid 50, possibly 60. So if I understand correctly, having a lower TA then would be less desireable to maintaining water balance...targeting toward 80 would be preferable.

Using acidic sources of chlorine is not an issue for me, it's bleach all the way when necessary.

[chem geek]

You are correct about the TA level when you have CYA, but you won't have to change that manually. When you increase your CYA the TA will increase automatically by about a third of the CYA level. So if you get down to a TA of 60 and then later change your CYA from 30 to 60, your TA should rise to 70 automatically. The recommendation of not going below a TA of 80 was for a CYA level of 70-80. It's not a "hard" limit, but more of a judgement call to ensure still having enough TA in case of something getting into the pool that could lower the pH.

Richard

[dawndenise]

OK, got it!:) Thanks much.