PH/FC lowering next day

[Fugazi]

I have a new 347 gallon Spa
My PH was really high 8.2 ish with jets full blast by Taylor drop test
The dealer had given me ph down granules
I was trying that but it wasn’t making a dent
So I changed to Muraiac acid
And added 1 oz every 30 min till I reached 7.6 while jets full blast
Then the next afternoon I tested it and it was 7.2 with the jets not running. 7.8 with jets running

Is this normal to have a big difference ?

Also the chlorine was 3.5 and we used tree spa for an hour and the next day the FC was .5

I don’t know what the CC is as my reagent ran out and I’m waiting for my new kit to arrive.


Why FC drop so much?

 

[newdude]

Why FC drop so much?

Oooooooh. Lotsa stuff. Sweat, body oils, bodily fluids, exfoliated skin, laundry sauces, shampoo, conditioner, soap, bacteria, a few drops of hot wing sauce still on your hands from dinner, and half a beer. And I probably missed 20 things. But yeah. You're making people soup.

All those things may take quite some time to be stirred up and sanitized. SLAM after soaks and check the next day to ensure you still have enough FC to remain well above minimum.

Then the next afternoon I tested it and it was 7.2 with the jets not running. 7.8 with jets running

Aeration raises PH and hot tubs are the kings of aeration.

 

[Methuselah]

How many people is we?

My tub burns through about 5 ppm of fc per bather hour. Is there any CYA in it? (How much)

 

[Fugazi]

How many people is we?

My tub burns through about 5 ppm of fc per bather hour. Is there any CYA in it?

it was reading 0 cya at the pool store, I’m waiting for my kit to come in as I ran out of cya test)

It’s two bathers wife and me
We usually do 1 hr
The spa is under a covered patio that has no sunlight hitting it and the cover is on during the day other than me adding chems and having it off when I run the jets

 

[Methuselah]

When my better half and I are in for 15 minutes it's 30 total(edit: minues, or .5) bather-hours and at 5 ppm per, uses 2 to 2.5 ppm fc (5 per bather-hour). This at 515 gallons, no bathing suits.

Your situation, 2 bather-hours, less water, maybe 6 ppm per bather-hour? More? I'd get some CYA in there, push fc to the high end of the chart, and dose a little while in there if necessary.

On the 7.2 vs. 7.8 PH, test without it running the jets. Aeration (turbulence) helps raise PH - but I have no clue if the small sample of turbulent water represents the PH of your tub.

True what you said about having the tub in the shade, but there are special needs when the equivalent of 2 people sweating in 100 degree hot tub water is like 50 to 100 people in a swimming pool. I'd suggest reading the sticky at the top of this forum.

 

[newdude]

True what you said about having the tub in the shade, but there are special needs when the equivalent of 2 people sweating in 100 degree hot tub water is like 50 to 100 people in a swimming pool.

173.5 gallons per person is

57.6 people in 10k gallons
115.6 people in 20k gallons
201.7 people in (my) 35k gallons.



FC is not only safe up to and including SLAM level, it's utterly needed to be kept 'high' during and after spa use as so much of it will be depleted.

 

[Methuselah]

173.5 gallons per person is

57.6 people in 10k gallons
115.6 people in 20k gallons
201.7 people in (my) 35k gallons.



FC is not only safe up to and including SLAM level, it's utterly needed to be kept 'high' during and after spa use as so much of it will be depleted.

Ratio, yeah ... so difference between mine at 515 gallons and @Fugazi's 347 gallons equates to 7.4 ppm per bather-hour. So it's trying to burn through about 15 ppm of chlorine with only 3.5 in the tub.

I'm no expert, but with zero CYA, I can't see making that work very well.

Hopefully we'll attract some expert opinions (I dare say that includes @Newdude).

 

[newdude]

I'm no expert, but with zero CYA, I can't see making that work very well.

Well the CYA is much less of a player in a hot tub that's covered for most of its life and mostly free of UV loss. It does however buffer the higher FC needed for bather comfort, so we still rec getting it up to 30.