How to maintain pH and total alkalinity in hot tub

Modawg2k

Well-known member
May 4, 2013
338
Phoenix, AZ
#1
I have a 450 gallon aboveground hot tub. what's the best way to maintain pH and total alkalinity. I've been using muriatic acid but I did not know if that's the best way since so little is used there is greater room for error.


Sent from my iPhone using Tapatalk
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,644
Tucson, AZ
#6
Ok. So here's what I would suggest.

-Continue to use MA to adjust pH; if low measurement volumes are an issue, then use the slightly more expensive but less concentrated 15% MA as that will roughly double the amount you have to measure out and put in.

- Since you are using tablets, I would be hesitant to keep your TA too low as the tablets are acidic and could cause issues. Keep your TA around 80ppm and monitor it. Bleach is not going to affect your TA much so shocking with bleach to get the Br up is ok.

- Add 50ppm borates to the water and try to use boric acid if you can get it (Duda Diesel sells it on their website and through their amazon page). The borates will help to control the pH rise from aeration.
 
OP
OP
Modawg2k

Modawg2k

Well-known member
May 4, 2013
338
Phoenix, AZ
#7
Great thanks.

My current numbers today after my fill this past weekend.

TA 90
pH 8
FC 0.5 (which if I understand correctly, puts my Bromine at 1.125 after multiplying by a factor of 2.25)

Plan of action
1) Lower TA to 80 by dropping pH
2) On a weekly basis, bump up my Bromine to above 10 as a shock
3) Look into borates to control pH rise

Is the weekly shock something that I should be doing? The bather load on this spa is very minimal.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,644
Tucson, AZ
#8
Maintaining a consistent bromine level is what you should be focusing on. Theoretically speaking, if you were able to maintain a constant bromine level, say 3-4ppm, then you would never need to "shock weekly". The only way to maintain a consistent bromine level is to either have an ozone generator to regenerate the bromine or use a tablet floater and keep it full of BCDMH tablets. If your tub's sanitizer is bottoming out a lot, then you definitely to shock periodically and before use.

Does the tub have an O3 generator?


Sent from my iPhone using Tapatalk
 
OP
OP
Modawg2k

Modawg2k

Well-known member
May 4, 2013
338
Phoenix, AZ
#9
I'm 93% sure it does have an ozone generator. I'll double-check with the manufacture. If I do have an ozone generator, is there any reason to continue to float bromine? I've been doing that the past year or so, throwing in just a few tabs here and there.
 
#10
I switched over my swim spa to Bromine and can't be happier. Maintaining bromine at 3-4 with a floater. I purchased MPS for shock after heavy pool use (2 people exercising) but wondering if I should switch to Cl instead. I was having problems with high pH but now my pH is dipping to 7-7.2. What does MPS do to pH compared to bleach?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,644
Tucson, AZ
#11
I switched over my swim spa to Bromine and can't be happier. Maintaining bromine at 3-4 with a floater. I purchased MPS for shock after heavy pool use (2 people exercising) but wondering if I should switch to Cl instead. I was having problems with high pH but now my pH is dipping to 7-7.2. What does MPS do to pH compared to bleach?
MPS is net-acidic when added to the water (lowers pH). Bleach will initially raise pH because it contains excess lye from the manufacturing process but that pH rise should be lowered over time as bromine chemical reactions are acidic. Your tablets are also acidic as well which is why you pH is going down.

If you plan to use tablets then you need to monitor pH and TA closely and add back alkalinity (using baking soda) as the TA decreases. Baking soda will also slowly raise pH as carbon dioxide outgases from the tub.


Sent from my iPhone using Tapatalk
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,644
Tucson, AZ
#12
By the way, I would not use MPS. It is no better than chlorine (and in some ways, not as good), it is more expensive than chlorine AND it adds sulfates to the water which can shorten the life of certain heater elements.

If your swim spa has heavy use, then you might consider adding a UV system to handle the extra bather load. Ozone would be good too as that would help regenerate the bromine but those systems are often woefully under-powered.


Sent from my iPhone using Tapatalk