Water chemistry after after drain/refill (bromine spa)

[bbrock]

Hi TFPers,
I was probably way overdue for a drain/refill on my 300 gal. above ground, stand alone spa. Prior to doing the drain/fill, I followed the directions and used Ahh-Some to kill any serious bacteria that was not killed by regular sanitation. After the treatment, was eye-opening to see all the bacteria and scum line that formed. Glad I used that stuff to kill anything thriving in the plumbing.

I followed the directions here at TFP for the 3 step bromine system, which uses a bromine floater. I attempted to balance my water chemistry before starting my bromide bank. I tried to adjust the pH from >8.2 with 31.45% MA, but doing so also lowered my TA. So, I added some baking soda to bring my TA back up. But, then after some additions, running the jets, and subsequent retesting, I noticed my pH was up again. So, I decided I was not going to sweat it and get caught up in a pH/TA dance. I added 1.5 oz (which was for 300 gal.) of my bromide starter, shocked it with 90 ml of 12.5% chlorine (I used 90 ml b/c I did not want my Br going sky high), and later I threw in my bromine floater.

Here are my #s from today. I was not going to treat the pH but rather let it naturally fall due to the net acidity effects of the bromine tabs. But, perhaps it will take too long.
Water temp 101 degrees
pH 8.0-8.2 (somewhere in there)
Br 6 (tested with the OTO test)
TA 80
CH 125

My CSI is about 0.36 right now, which may be a little high. Generally, over time w/ the evaporation and water additions, my CH will/would increase.

Questions:
1. Should I bother manually lowering the pH, which will also bring down my TA? Don't think I want to/ought to have my TA go lower.
2. With the old water, I was shocking 1x/wk with about 75ml of 12.5% chlorine. With my brominator open at about 2.5-3, the Br level would eventually drop to about 6-8 toward the end of that week. I shocked with 90 ml of 12.5% chlorine on 6/12, and with my brominator open at 4, my Br is just at about 6. What is going on? Do I have to activate more bromine from my bromide bank?

Tx.

 

[pooldv]

I can't help with the bromine part.

For PH and TA
I would lower TA to 50 and add 50 ppm of borates to help stabilize PH. This process better covers the PH/TA/borate part of hot tub maintenance, How do I use Chlorine in my Spa (or pool)?

 

[bbrock]

Tx for the reply pooldv.

I guess I could lower the pH, which would lower the TA, and see what happens. It's always quick and easy to increase, if I need to, by adding some Na Bicarb (baking soda).

I assume over time I will see the pH drop b/c bromine is acidic. Maybe it is not happening right now b/c my water contains more bromide vs. the active bromine.

I really don't want to add borates to the spa b/c I don't want another thing to have to test and/or buy testing supplies for.

 

[Brian VT]

I was under the impression that borates are just a one-time addition at water change, just like the bromide.
I don't test for borates. I assume it's still in there doing it's job because my pH stays fairly consistent.

 

[bbrock]

Brian VT, tx for the reply. Do u use bromine?

 

[pooldv]

Brian is correct, it is just a one time add 50 ppm. Then do it again next time you drain and fill. I use borate in my hot tub and my pool. I have borate test strips but I never test my hot tub and only test the pool once or twice each spring. I've had the same bottle for 4 years now.

 

[Brian VT]

Brian VT, tx for the reply. Do u use bromine?

Yes.

 

[bbrock]

Thanks Pooldv and Brian VT. I appreciate all your help. So, I did some 31.45% MA additions and got my pH down. The TA didn't drop as bad as I expected. pH now at 7.6 and TA 60. This is manageable. Yesterday I also added about 50 ml of 12.5% chlorine as my Br was 3.375 when tested w/ the FAS-DPD method (and 4 when tested with the OTO method). I now the range is 4-6. When I tested later last night, it appeared the Br was 10+, but when tested today w/ the OTO method it was 6. Either I could not get a good read last night b/c it was dusk, perhaps I have not activated enough of my bromide bank, my bromine tabs are not good, or the Ahh-Some water treatment is having some residual effect on my current water. It is odd my bromine level is not stable even with my bromine floater open at 5. On my prior water, I never had to open it to 5-6 unless I went on vacation. Regarding my bromine tabs, I think they are fine b/c on my old water they maintained my bromine level adequately.

I did not add borax yet to add 50 ppm borates to the water. I wanted to first ask you Pooldv and/or Brian VT about your experiences with having added borates. Did either of you notice a significant difference with your pH stabilization after having added the borates? Did you see less pH rise and drops? To add 50 ppm borates Pool Math shows me to add 17 oz by volume of borax and 8.4 oz 31.45% MA to counter the pH rise. If I did that, I would just hate to see my TA and pH get too out of whack in that I would have to then compensate further for that. Brian VT, you're using bromine, so I would definitely like to know what effect it had on your pH. Also, is your spa acrylic or plaster? I want to rule out extraneous variables from the comparison of my situation to your experience, but I know that is not fully possible.

Lastly, since my spa is acrylic, and keeping a negative CSI, Pool Math shows that I am getting close to "potential to become corrosive to plaster." I don't have to worry about the plaster part since I have acrylic, but I think Chem Geek responded back to one of my threads one time in that the concern with too negative of a CSI would be corrosion to metal. Can anyone refresh me on this? Is that the case? I don't want to cause a problem with corrosion to the heater.

 

[bbrock]

I will answer my last question. I performed a quick search here at TFP re: negative CSI and metal corrosion. Came across this excellent thread (Negative CSI and metal corrosion) even if it is above my pay grade Sounds like negative CSI is not an index that correlates with metal corrosion. And, that metal corrosion doesn't become an issue until pH gets to around 6.8. Therefore, in my situation, I think there is not a significant risk for metal corrosion (i.e. of the heater).

 

[bbrock]

Upon further analysis, if my spa will eventually encounter pH drop d/t the net acidic effect with using bromine tabs, could the addition of borates to the water help slow the drop? Or, do borates only really help prevent pH rise?

This thread (Bromine Use In a Spa) and some other reading/searching got me thinking/curious if the addition of borates to a bromine spa is safe. I already know that is consumed in the spa water is consumed in large quantities that it may pose a safety hazard, but the amount that must be consumed is quite a bit (as informed to me previously by Chem Geek). But, with the addition of borates, does that change the equation/concerns?

P.S. anyone know where Chem Geek is? I could benefit from his vast knowledge on this topic/my questions

 

[pooldv]

It is better to keep PH at 7.2 and up and avoid 7.0, especially for any length of time to avoid metal corrosion.
Correct you do not need to worry about negative CSI as a corrosive factor.
Yes, borates stabilize PH in both directions.

 

[bbrock]

Happy Father's Day all you Dads!

Tx Pooldv for your response and pm. Have not elicited many responses.

Spa chemistry still funky. Br today is about 5, and pH climbed back up to 7.8 (maybe higher; hard to read). I am really questioning why my pH is climbing vs. dropping. Bromine tabs cause a net acidic effect and should be causing the pH to drop. Therefore, I thought of the following questions/concerns:

1. I am 99% certain I added Na Bromide after my drain/fill. But, may be I forgot in my haze. Is there a specific way I can test or determine if I added my Na Bromide bank?
2. Does Na Bromide expire? I purchased a 16 oz. (1 lb.) bottle a couple years ago, which is what I used. I am quite certain that it Na Bromide doesn't expire or lose efficacy.