ph question

[TIMMAH]

i'm using 3 stage bromine.
a hour ago my tub had a ph of 7.2 after sitting and 7.5 after use. that is with a 60 alkalinity. i've bumped the alkalinity up to 70 a few time but after a week or so it's back down to 60. i just added ph up and i ment to bump it up to around 70 but i got 80 with a aerated ph of 7.8 witch gives me a water blance of +.09


here is my question.
is it better to have a 7.2 ph and when the tub is aerated a ph of 7.5?
or would a ph of 7.4, 7.5 with a rise to 7.8 when aerated be better?

 

[duraleigh]

If it was your pool, I would suggest your are fine tuning a bit too much. Within the 7's is just fine for pH.

I am not a spa expert so one of the spa folks may have a different take.

 

[TIMMAH]

i don't get much ph change in the pool. it's more or less set it and forget it.
the spa is pretty stable with just a .3 jump when i run the pumps. i've been shooting for a 70 alkalinity with a drop to 60 when i add more ph up. but was wondering if maybe i should be shooting for 80 alkalinity and boost it when it hits 70.

60-70 alkalinity is low 7's ph and 70-80 alkalinity is high 7's ph

so is it better to have the spa sitting at 7.2 ph for a few days with a peak of 7.5
or 7.4-7.5 with a peak of 7.8 or 7.9

 

[chem geek]

I'd go with the latter since the rate of pH rise should slow down at higher pH so you'll need to add less acid. So when you lower it, have it go to 7.4 or 7.5. During use, it's fine to have it rise to 7.8 or so and then lower it afterwards. The only reason to avoid a higher pH is if you've got a high CH (250+ which at spa temps is high) or if you've got metals in the water that can cause staining.

 

[TIMMAH]

chem geek are you saying my ph shouldn't move? it goes up when i use it and comes back down by itself. then over about a week or two it drops more and i have to add ph up. i'm guessing if i use borates then the ph would be more stable.

the other day ph was at 7.2 and alkalinity 60. after mixing in ph up by running the jets it was 7.8-9 and alkalinity 80. the next day ph was at 7.5 before use and 7.8-9 after running the jets for 20 minutes. then the next day it's back to 7.5ph before use. if i don't use it for a few days the ph would stay at the before use ph reading.

but i think you answered my question. keep it at 7.4-5 ph reading before use.

 

[chem geek]

The pH should not be dropping unless you are using an acidic source of sanitizer. If you were using a hypochlorite source of chlorine, then the pH should not be dropping over time. What are you using? Trichlor, Dichlor, bromine tabs, non-chlorine shock (MPS)?

 

[TIMMAH]

i'm using 3 stage bromine. it's the first line in my first post. i'm using bromine tabs with dichlor in them. i shock with bleach or MPS, i'm using up what MPS i have left.

 

[chem geek]

Ah OK then. The bromine tabs and the MPS are both net acidic so when using them you can set a TA a little higher where the pH averages where you want it. It sounds like you've got a reasonable handle on things. When you stop using the MPS, you may notice the pH drifting up more and can let the TA drop (from acid addition) to help compensate for that.

 

[JamesW]

i'm using bromine tabs with dichlor in them.

To avoid any confusion, the "dichlor" in bromine tabs would be 1,3 Dichloro-5, 5-Dimethyl-hydantoin and/or 1,3 Dichloro-5, ETHYL-5-Methyl hydantoin, and not Sodium Dichloroisocyanurate dihydrate (aka Sodium Dichloro-s-triazinetrione Dihydrate), which we normally refer to as "dichlor".

Granular bromine is a combination of Sodium Dichloroisocyanurate and Sodium Bromide.

 

[TIMMAH]

what is the difference between the two?
the granular bromine that i have said it's bromide and Sodium Dichloro-s-triazinetrione Dihydrate. so since the tabs said they had 29% chlorine in them, i just assumed it was dichlor.

i just bought 8 lbs of granular Sodium Dichloro-s-triazinetrione Dihydrate. i was going to use it to boost bromine levels and to shock when needed. cya in the dichlor will not stop the chlorine from changing bromide to bromine even at high cya levels right?

 

[chem geek]

I'm sorry this is so confusing. The bromine tabs you are using are the most common kind and are 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH) so contain both chlorine and bromine bound to DMH. It's best not to call it bromine with Dichlor since "Dichlor" refers to a specific chemical of two chlorine bound to Cyanuric Acid (CYA). The chlorine in this BCDMH tab product will convert bromide in the water to bromine, assuming some bromide is already present as with the 3-step bromine system where you initially add some bromide to the water. Over time, bromide will build up as used-up bromine becomes bromide.

The granular bromine you have is a combination of two separate chemicals -- sodium bromide and sodium dichloro-s-triainetrione dihydrate, the latter aka Dichlor. The Dichlor in this product reacts with the bromide (after dissolving in water) to create bromine.