Winter TA/PH battle

[Scottie_In_IA_1981]

I can't say that this seems that strange or unreasonable to me, but I'm adding at least 2 tbsp of dry acid to the tub every other day it seems.

I am maintaining a 300-ish gallon custom tile/plaster hot tub all year long and have noticed the need for a very altered strategy when the dead of winter hits.

With the freeze protection, the filter pump and the jets pump will start kicking on automatically.  When temps outside fall below 20 degrees Fahrenheit or so, both pumps will run 24/7.

I was just curious what others might be experiencing as far as water evaporation in these temps.  There doesn't seem to be hardly any need to add water over the summer, the half gallon or so I use to dilute the bleach every time I add it (every 1-2 days) seems to be plenty to keep the water level where it needs to be.  In the winter however, negative or just above zero degree temps are pretty typical here for about a month or two.  Obviously you can 'see' the steam rising off at these temps...even with the lid on you can see the little bit of steam leaking out.  So, I am betting that the dry colder air (in contrast with the 104 degree water) will cause a lot more evaporation than the warmer temps of summer (during which I actually have the hot tub water set around 89 degrees).  So, at these low temps, I seem to be adding about 5-10 gallons of water every few days at least.  

My question here is mostly centered on the TA/PH impact of these altered conditions.  The water I add comes from a well and runs through a whole house filter and a water softener...so, although I'm not really adding hardness to the water when topping it off, this water has a pretty high TA initially (probably around 300 ppm or more).  So, adding roughly 20 gallons of that water to a roughly 300 gallon tub every week...even if the tub had a perfect TA/PH, I'm going to have to constantly chase it back down because of the added high TA water used to top it off.  Does this sound right, or should I be having better luck being able to stabalize the PH without having to add this amount of acid every 2 days?

In the summer, once the TA/PH is stable, I can get away with keeping an eye on it maybe once a week.  In the winter, it seems to need constant attention.  I use the Dichlor then Bleach method, so I have got accustomed to having to test and add the sanitizer every day or every other day...and so, not a huge inconvenience to also just top off the evaporated water and add acid.

Also, it seems I have little choice here, the ph is constantly going to be jumping between 7 and 8.  I knock the ph down to 7, the pumps run 24/7, I add high TA water to top off evaporated water, and even within that 2 day span the ph is going to be back up to 8 or above.  Since there was an initial level of calcium increaser added upon filling because of having the plaster tub, is this constant fluctuation of the calcium saturation index due to the constantly fluctuating ph going to invite problems with scaling?  I suppose if the CSI is fluctuating between just below zero and just above...then the long term issues of having it positive and causing scaling could probably be avoided for the most part?

So, again, is there a better way to stabalize here?...I have never added borates, but don't know that doing so would lend itself to this issue very substantially...?  Or, perhaps this is just a common winter issue for people living in these colder areas?

[RDspaguy]

I think you're looking for @waterbear.😉

I will say this, however. 

A good, tight fitting cover is your best defense against evaporation loss, but it can only do so much. Increased loss in winter is normal.

Aeration raises ph. If it's running more you'll get more aeration. Close the air control valves if you have any.

 

[waterbear]

5 hours ago, Scottie_In_IA_1981 said:

Does this sound right, or should I be having better luck being able to stabalize the PH without having to add this amount of acid every 2 days?

Sounds about right. Because of the freeze protection the pump is running more and that means more aeration of the water which means more outgassing of CO2 which means faster pH rise. SInce your fill water has a high TA that adds to how fast the pH will rise. SInce you can't really control the TA or pump run time/aeration in the winter your only factor that is under your control is where you put the pH. The lower the pH the faster it will rise so I would suggest going no lower than 7.6 and don't worry about lowering it until it hits 8.0. I would also recommend adding 50 ppm borate which will introduce a secondary boric acid/borate buffer that helps keep the pH in the 7.7 to 7.9 range for a longer time than without the borate

 

5 hours ago, Scottie_In_IA_1981 said:

I knock the ph down to 7

Don't do that. It's a big part of your problem. No lower than 7.6!

[waterbear]

THE MAIN CAUSE OF pH RISE IN A POOL OR SPA IS OUTGASSING OF CO2.

THE HIGHER THE TA (CARBONATION IN THE WATER), THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WILL RISE.

THE HIGHER THE AERATION OF THE WATER (OZONE SYSTEMS, SALT WATER SANITIZER SYSTEMS, AIR INJECTORS,  AERATION FROM YOUR JETS, 24 HOUR CIRCULATION ON HIGH SPEED, ETC.) THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WILL RISE.

THE LOWER YOU PLACE THE pH THE FASTER IT WILL RISE (YOU ARE CONVERTING MORE BICARBONATE IONS, WHICH IS WHAT WE MEASURE AS TA,  INTO CARBONIC ACID, ESSENTIALLY CO2 DISSOLVED IN THE WATER.

[Scottie_In_IA_1981]

Thanks for the prompt replies!...this forum is grade A.  

I figured borates were part of my answer here.  I will see how things go once I've addressed adding the boric acid, as that seems to be a smaller/easier part of my solution.

As far as me shooting too low on the PH though...although I'm sure your answer is correct, I guess I'm still trying to wrap my mind around it a bit.  

So, as far as 'the higher the TA the faster the PH rise' and 'the more aeration the faster the PH rise'...these already made pretty good sense to me...but I guess maybe I wasn't taking into account or completely understanding that it's also 'the lower the PH the faster the PH rise'.  

Now, could one safely say that the reverse to all of these is also true?...that 'the lower the TA or amount of aeration the slower the PH rise' (both of these would make sense to me) and also 'the higher the PH the slower the PH rise'?  Or, if the TA is 'too low' (which I've never had an issue with), would that mean that the PH would not only be 'rising slower' but could also be lowering in the other direction, in which case you would be having to chase the ph back up with a 'PH Up' product?

The ideal situation would be to achieve a TA where there is some longer term PH stability...like, a sweet spot where the PH is hovering closely around that ideal 7.8 range.  Obviously that PH isn't going to last forever, even in the summer...but the stability is going to largely depend on those 2 things (the TA level that is maintained, and the amount of aeration), correct?  What I'm curious about, is whether any amount of longer term 'stability' is even achievable with the constant aeration that I'm getting...in other words, even if you took out the variable of the higher TA water that I'm adding because of evaporation, would there ever be a 'sweet spot' where I could sustain a good PH for more than a couple days with all that aeration?  Or, would that aeration just continue driving up the PH past what is ideal regardless of where the TA is at?

I apologize if I'm missing something that seems blatantly obvious or if I've overthought this more than I need to.

And, just speculating for now...but instead of adding the acid along with the X gallons of water that have evaporated 'every other day', it's sounding like I need to add that smaller amount of each that would be necessary EVERY day.  That was sort of what I was looking to avoid if at all possible, having that chore out in the cold every day instead of every 2 or 3 days.  And, again, I will see how things go with the borates and not shooting so low on the PH.

If I'm thinking about this correctly, what you're saying is that I've been overshooting that sweet spot by lowering the PH too far?  So then, it just bounces back up quicker...kinda like putting more force on a yo-yo.  I suppose, if I continued doing so, that's not really buying me any longer term stability huh?

Thanks for any and all of the help here, I'm sure things will click and I'll figure out the best strategy eventually...I probably just haven't let the knowledge of these replies completely soak in yet.  Worst case, I just accept the fact that the hot tub absolutely needs daily attention over the winter months.

[waterbear]

Read this post on lowering TA. It explains the chemistry in layman's terms.

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

 

In a nutshell, what we call Total Alkalinity (TA) is a carbonic acid/bicarbonate buffer system. It's main purpose is to keep the pH from crashing, which is important when acidic sanitizers /oxidizers (dichlor, trichlor, MPS) are used. The lower the pH the lower the bicarbonate ions since more of them convert to carbonic acid. Carbonic acid will gas off and the net effect is pH rise since the amount of acid in the water becomes less as the CO2 gases off.  The lower you put the pH the higher the level of carbonic acid. This means faster outgassing of CO2 and a faster pH rise as that occurs.

The boric acid/borate buffer system has a complementary effect that effectively 'locks' the pH around 7.7 for a longer time than without it. If you do add borate  maintain the pH in a window of no lower than 7.6 and don't lower it until it hits 8.0. (I would recommend adding borate with boric acid since it will have minimal impact on pH by lowering it slightly and it will rise on it's own, and it does not require adding muriatic acid to offset the high pH created by adding borax. the only disadvantage is the slightly higher cost when compared to borax and muriatic acid. It's still much cheaper than the commercial borate products for pools that are pH neutral (since they are just a mix of boric acid and borax).