HIGH alk!

[giulietta1]

Filled the spa yesterday and tested the water before adding sanitizer. My TA was 280! I think pH was about 7.3; CH about 300. Can I use dry acid to lower alk in the same way one uses muriatic in a pool, or does that not work?

This morning my pH was on the high side, say 7.7. But the water was quite warm, and I read later this morning that temperature affects the pH test. Should I let a sample cool to room temp and then test the pH?

OOOOhhh! It just occurred to me that since I shocked last night, the bromine level was probably still pretty high. I know high chlorine levels interfere with the pH test--does high bromine do the same thing??

Since I'm using bromine which is rather acidic, that is purported to "eat" alkalinity. . . perhaps I should just monitor the alk and see if the bromine brings it down??

 

[chem geek]

Yes, high bromine levels, just like high chlorine levels, can interfere with the pH test. You can add a drop or two of thiosulfate to remove such interference, but that will tend to increase the pH by about 0.1-0.15 per drop so keep that in mind.

As for temperature, I do not believe the pH test is as affected very much by temperature, but you can always test one sample immediately and then do another test (after thoroughly rinsing the container) letting the water cool to room temperature and see if you find a difference (let us know, since such information is helpful to others).

And yes, you can use dry acid (sodium bisulfate) to lower your pH and follow the procedure to lower your alkalinity by keeping the pH low (around 7.0) by adding acid as needed and aerating which should be easy to do in a spa (i.e. with jets). Then when you reach your TA target, stop adding acid and continue aerating until the pH goes up to where you want it (probably around 7.5).

Not all sources of bromine are acidic and generally once you have some bromine in your spa you mostly just reactivate bromide to bromine by using chlorine or non-chlorine shock (KMPS). In any event, an acidic source will not lower your TA by itself -- only a low pH combined with aeration will drive off the carbon dioxide that will truly lower the TA.

 

[giulietta1]

Hmmm. . . just one more example of something WRONG in the Taylor guide book. That's where I read that bromine tends to lower alk.

 

[Guest]

They are referring to the most common form, which are the tabs. Also, most people use MPS to shock a bromine system and that is acidic. If you are using a 2 step sysem with sodium bromdie and liquid chlorine (or bleach) then you will probably want to run a lower TA than if you are using tabs and/or MPS.

 

[giulietta1]

I learned that it is EASY to lower the TA in a spa! Almost too easy; after lowering the pH and then aerating (running the jets) for an hour or so, the pH was actually up above 8.0. In just a couple of steps I had the alk down to about 140. Later it went down more, to about 110-120.

I'm using bromine tabs in a dispenser. Just used the granular stuff as a startup. I used MPS shock last night.

:?: Does MPS interfere with both the free and combined chlorine tests, or just the combined? I'm using a FAS-DPD chlorine test for the bromine, applying the correction factor to get the bromine #'s. If the MPS only affects the combo reading, does that mean I don't have to worry about it? Or should I get the deox reagent?

I'll get the deox reagent eventually, since I would like to use the MPS in the pool also. Just wondered if I ought to go ahead and get it now.

 

[giulietta1]

pH and water temp

I wanted to put this info by itself, since I think it could be very useful! I tried testing the pH of the warm water fresh from the spa, then I let the water sample sit until it cooled to room temp. I tested pH again on the cooled water. I obtained the same pH reading both times!

 

[Guest]

guilietta1, a few bits of info for you.
1) pH test is NOT temperature dependent (but some of the other tests can be!)
When testing bromine you only test total bromine. That is why there is a separate FAS-DPD test for bromine. IF you want to use the multiplier of 2.25 and a chlorine test then you need to use a Total chlorine test such as OTO (Taylor K-1000) or DPD total chlorine (Taylor K-2005). The FAS-DPD test does not test total chlorine. It tests free chlorine and combined chlorine!
MPS interferes with total chlorine which is important because you want to determine the amount of combined chlorine in the water. With bromine it's a moot point. The MPS is oxidizing the bromide into active bromine sanitizer so it's not staying in your water! (Nor would chlorine if you decided to use that for shocking!) Once again if you are testing bromine with an FAS-DPD test you need the right test so you can get a total bromine reading! The bromine test does not use the same reagents as the free and total chlorine tests do!

 

[giulietta1]

I'm trying to avoid spending lots of money on more test kits. I know that total bromine only is the thing to test; I bought a cheap test kit that purported to test chlorine, bromine, and pH. It only came with color standards for chlorine & pH, not bromine. :x So I am trying to work with what I have.

 

[Guest]

When you consider how much your pool and spa cost you (it was in the thousands of dollars!) it it really a lot of money to spend even a few hundred on decent test kits? (and the reality is that it will cost you much less!)
The Taylor K-1517A FAS-DPD test kit for bromine is only $21.35 on their website. Since you alreay have the K-2006 you have the pH, TA and Calcium Hardness tests that you would need for the spa already. NOT a big expense!

 

[giulietta1]

Ok, ok. . . <sigh> I will spring for it. It will have to wait until Friday's paycheck, tho!

Looking at Taylor's website, I could get the FAS-DPD titrant for bromine, which is all I need to add to my kit to have a bromine test. Already have the DPD powder, which is the same stuff for testing Cl or Br. That would cover both Cl and Br, and would be only 11.05 for a 2-oz bottle.

 

[Guest]

Just rememeber that when you test bromine it tests as 1 drop is .5 ppm for a 25 ml sample and 1.25 ppm for a 10 ml sample (unlike the chlorine test which is .2 ppm and .5 ppm per drop.)

 

[giulietta1]

Yes, I will make sure to print out those instructions to keep with my kit! The cheap test kit works; it's a DPD test, but it's not very precise. It has standards for 3.0, 2.0, 1.0, etc., and those are for chlorine! Which means I have to multiply that estimate by 2.25 for bromine, compounding the imprecision. :? It will do until I get the new reagent. I believe I have my dispenser properly adjusted now. I've started adding the borax and will put in the rest tonight.