Vacation, Trichlor tabs and PH

[Wildcat]

I have my CYA around 30 in hot (110 degrees) Tucson. Going on a weeks vacation. Have not used tabs in over two years and I am comfortable using tabs for this week as 3-4 tabs will raise CYA to 40 or so in 10,000 gallon pool. I actually let CYA drift lower so I could do this, I actually think 40-50 is better here.

My question is PH.
In Pool Math says 3 tabs will lower PH by approximately .88. That sounds like a lot of PH lowering. If I start out with 7.5 (and TA of 80) will it really lower it to 6.62? Or am I misreading the .88? I sort of asked a similar question a while back and not sure I understood the answer (and can't find the thread)
I realize that in my pool PH naturally drifts upwards but still 6.62 is very low and I will not be here to adjust it. So while the FC and CYA it will add is about spot on the PH drop won't work, right?

 

[BoDarville]

You are reading the 0.88 decrease in pH correctly. However, that decrease will be offset to a significant degree by the aeration from your waterfall. I have also used pucks when I'm on vacation and it has worked out well. Like you, I have aeration (from a spillover spa), so pH never got below range and I usually started out with a pH of 7.5 - 7.6. However, if you are that concerned, you could increase pH slightly towards the upper part of the recommended range to give you a little more headroom.

 

[Wildcat]

You are reading the 0.88 decrease in pH correctly. However, that decrease will be offset to a significant degree by the aeration from your waterfall. I have also used pucks when I'm on vacation and it has worked out well. Like you, I have aeration (from a spillover spa), so pH never got below range and I usually started out with a pH of 7.5 - 7.6. However, if you are that concerned, you could increase pH slightly towards the upper part of the recommended range to give you a little more headroom.

OK, thanks. I generally don't run the waterfall unless we are in the pool as I have popups and it takes some from their velocity. I will run it the next couple of days to bring PH up and dial back the number of openings on the floater. I plan to bring FC up to or slightly above slam level so FC should be OK by my calculations.

Any idea how much TA drops? I keep mine at 60-70 to make it easier to keep a stable PH (which has worked) and to keep CSI low (CH or 540 or so). Maybe I should raise it to 80-100?

Note: based on the numbers I plug into Pool Math I think I will run the waterfall a little. Hard to keep things balanced when I an not here to fine tune. Maybe I am overthinking this.

 

[smackdab]

Trichlor doesn't lower the TA but it is acidic. That was explained in another thread somewhere around here. If your TA is too low the pH will drop instead of rise. 90 TA holds steady in my pool with 3 or 4 trichlor tabs floating but without the tabs it holds steady at 70 TA. At least now you have a reference to go by.

 

[Wildcat]

Returned from vacation a few hours ago. Must have had a pretty good rainstorm as pool was almost up to skimmer top. Drained a couple of inches and tested.

I had dumped in bleach to bring FC up to around 20, PH was about 7.8. TA 90 or so.

Put four pucks in a floater and opened to four hole setting (on each side)

I would estimate about half the pucks gone in a week.

TA still 90, PH 7.4-7.5

FC at 11

CYA moved from 40 to 45 (we all know how precise CYA measurements are)

So it appears this was a successful vacation strategy. FC ended up a little high but better high than low.
PH drop was controlled. CYA increase was a about what I expected for the amount of pucks that were dissolved.

I am going to leave the floater in and let CYA drift towards 50. With the hot summer we are having I am more comfortable at 50.

The only thing I would adjust next time is either lower the dissolve rate to let less FC and CYA in depending on what I need at the time or reduce how much I raise the FC before leaving.
I did run the pump though about 40% less than usual.

 

[JVTrain]

Glad to hear it worked out!

 

[Wildcat]

Good thing I retested today and while FC was 8, PH 7.5, TA 70, CH 560 (just the way it is here with fill water high CH and lots of evaporation, controlling CSI)

CYA had been at 45 upon my return Monday but we had a lot of rain (early Monsoon season) and so had to do some draining.
Instead of CYA drifting up towards 50 it actually dropped to around 35! Threw 3 more pucks in, glad to be using them up