Another PH question

[Nitro]

Thanks Richard for that very informative post.

For the record, Richard (Chem Geek) has never claimed to me to be the first to come up with the Dichlor/Bleach method. I called him the creator because he did come up with it on his own. And as far as I, and many others are concerned, he is more knowledgeable on this method (and water chemistry in general), than anyone out there. So, I should have said the "Master", instead of the creator, which would have been more appropriate.

As for my above approach to lowering TA. Like I said, it's not my approach. I just took an existing approach that has been proven to work, and created a flowchart for it. That's what I do best, because I've been doing it for over 25 years, programming computers. I'm going to quote Chem Geek here, "I prefer to assume the chemistry is valid, then see what happens, then adjust the model if theory does not match reality.  So far, this has worked reasonably well.". As far as I know, the Acid/Aeration method to lower TA has worked well for everyone who has used it. However, if anyone can come up with a situation where it doesn't work, I'd seriously like to hear it, so I can adjust the model.

In the meantime let's help Brian (and others) learn to balance his water, which is the reason why we're here.

[kervis]

AWESOME!!  I haven't seen such a fabulous debate here in quite some time.  Good points-no name calling--great information--just excellent!  
Some of you know that I happen to have the same issues as Brian, thus I will have to re-read some of this later, and again later, and then again....

This thread will certainly impact how I care for my tub for years to come.  For me and my tub needs, it contains a wealth of info that I had not heard before.

For now, however, I shall grab a cold beverage and head out to my  tub with high pH, high TA, possible low calcium, and nice hot water.  Thanks, you guys!  

[brian_tr]

Merry Christmas All.

Checked water for first time in last couple of weeks.  PH 7.7 and alk 110.  Looks like its locked in now.  I have a 2002 sundance cameo.  The shell is in great shape.  No stains or scales.  This is how I have always done the water in the past until this last time:

Fill tub.  Power up to get air out of lines and shut power off again.  Slowly add 3 cups muraitic acid into water.  Let sit for 10 minutes and turn back on with jets running for 1 cycle.  When water heated up added half a bottle of cacium hardness.  Waited one week to check water balance and the ph and alk where always almost dead on.  I know this method drops the ph down for a little while.  I do not see any kind of damage to tub.  Is this method really that bad on tub?

[chem geek]

Merry Christmas!

If you are using full-strength Muriatic Acid (31.45% Hydrochloric Acid), then each cup in 350 gallons will lower the Total Alkalinity (TA) by almost 90 ppm.  So unless your fill water were extremely high in TA of say 350 ppm, then this amount of acid would make the pH dangerously low and remove the carbonate pH buffer from you water.  If the TA started out as 350 ppm, then the 3 cups would lower the TA to 82 ppm and the pH to around 5.6 though the pH would rise rather quickly from there.  However, if your TA were 270 ppm or below, then the pH would get to 4 or below and that's very bad; if the TA were 200 ppm or below, then the pH would get to below 3.

If your Muriatic Acid is half-strength (15%) then the TA would drop around 45 ppm with each cup so starting with a fill water TA of around 200 ppm would then have the TA drop to 81 ppm and the pH drop to around 6.0 and then go up from there.

It is not good to have the pH drop too much below 7.0 for an extended period of time.  You can have more rapid corrosion of metal and other parts of your hot tub.

[brian_tr]

Thanks for the responce.  I will try Nitro's method next time.

[chem geek]

Just out of curiosity, what is the pH and TA that you initially measure right after filling your tub and before adding any chemicals?  Also, is the Muriatic Acid you are using full-strength (31.45%) or half-strength (15% or so)?

[Nitro]

Not a good idea to add large amounts of acid without knowing your TA, and how much it will bring it down, even if it worked in the past. Your water could change on you, if your town/city changes it's water source i.e. (multiple wells, going from a lake to well etc.) It's ALWAYS best to measure TA and pH before adding anything. Then calculate how much Acid or Baking Soda you need to bring your TA to an ideal range which could be anywhere from 60-100. If you have high TA then you should use the Acid/Aeration method to lower it, so your pH doesn't drop too low (<7.0). If your TA is too low, it's just a matter of adding the correct amount of Baking Soda.

One Final Note, and this is often overlooked. The less you put into your tub, the longer the water will last, and the less hassles you'll have. If you are constantly adding acid then base etc etc, you're wasting chemicals, and shortening the life of your water. Not to mention making water balance more complicated than it needs to be. It's best to add the chemicals up front to get your water balanced, then fine tune from there. The key is to get your TA fune tuned, then your pH will fall in line. If/when you get good, you rarely need to add anything after the initial dose.

Merry Christmas!

[brian_tr]

It's been a long time since I had it measured right from the tap.  The ph is always maxed from what they can read and it seems like the alk was somewhere around 400.  The acid is 31.45.  

[chem geek]

Thanks for the info.  So if I start with a pH of 8.4 and a TA of 380 and add 3 cups of Muriatic Acid (31.45%) in 350 gallons, then the pH drops to 5.85 and the TA drops to 112 ppm which is about where you ended up.  As noted, the pH is too low though it won't stay that way for very long as it will rise fairly quickly from outgassing of carbon dioxide.

With your numbers, you could just add one cup of Muriatic Acid to start with as that would lower your pH to 6.7 which is tolerably OK and again won't stay that way for very long.  Your TA will then be 291 ppm.  You would then add smaller amounts of acid -- about 1/2 cup a two more times and then 1/3 cup three more times cycling with aeration to have the pH rise.  You will still end up using a cumulative total of 3 cups of acid, but you won't be exposing your tub to very low pH.  If you do it this way, then you will have the following:

380 ppm TA, 8.4 pH
add 1 cup acid
291 ppm TA, 6.7 pH
aerate
291 ppm TA, 7.5 pH
add 1/2 cup acid
246 ppm TA, 6.8 pH
aerate
246 ppm TA, 7.5 pH
add 1/2 cup acid
201 ppm TA, 6.7 pH
aerate
201 ppm TA, 7.5 pH
add 1/3 cup acid
171 ppm TA, 6.8 pH
aerate
171 ppm TA, 7.5 pH
add 1/3 cup acid
141 ppm TA, 6.7 pH
aerate
141 ppm TA, 7.5 pH
add 1/3 cup acid
111 ppm TA, 6.6 pH
aerate
111 ppm TA, 7.5 pH

Also don't forget to add the acid very slowly over a return flow with the circulation pump running.  I would keep the jets off while pouring to avoid having it splash back into your eye -- you should wear glasses or safety goggles for extra safety (acid in the eye can cause blindness).

Richard