Ph Help

[Botlefedpony]

OK So I have read through this forum and the last few days, I have always had issues with my tub so now I bought the Taylor kit and started fresh last night. Here is what I have now.

400 Gal tub

TA 50

PH 7.8

CH 220

My problem is when ever I run the pumps with the air my PH will go over 8.0, I let the tub sit over night and my readings this AM were

TA 50

PH 7.6

CH 220

This was before I ran the pumps at all, after running the pumps my PH went back to the 7.8 8.0 range.

Should I read the PH before I run the pumps and go with that reading or after the pumps have run?

My temp is up to 102 but I have not added any Bromine yet so I have not tested for that. Waiting to get the other numbers right first.

[chem geek]

If you want to keep your TA lower (i.e. at 50 ppm) which will tend to reduce the amount of acid you need to maintain the pH, then you should have a supplemental pH buffer such as using 50 ppm Borates (usually from boric acid). Aeration drives carbon dioxide out of the water faster and that causes the pH to rise. A higher TA would make the problem even worse since TA is a measure of the over-carbonation of the water

When you start using bromine you may find that the pH doesn't rise as much because the bromine tabs are net acidic (though not by much).

[Botlefedpony]

My problem right now is I can't get the PH to stay down, As soon as i run the air it goes back up over 8.0 I just added Gentle Spa as a buffer and the PH went through the roof.

[chem geek]

Gentle Spa is unfortunately not very pH neutral so you need to add acid to get the pH lower, but it should be more stable after that. I don't know why they don't use pure boric acid in Gentle Spa, but they don't. In the future, you can get pure boric acid granular from DudaDiesel or The Chemistry Store. 50 ppm Borates in 400 gallons, using boric acid, is 15 ounces weight (around 16 fluid ounces volume). You can use The Pool Calculator.

[lagreca]

I can second adding boric acid. I got all my numbers good, then added boric acid, and my pH has been LOCKED in since! Before it was doing as you said, after the jets were run, pH would be quite high.

I bought my boric acid from DudaDiesel, and it arrived quickly.

[chem geek]

Just note that after adjusting pH with the Gentle Spa you now have boric acid in the water, though I believe the dosage recommendation for Gentle Spa ends up with around 30 ppm borates while you could use 50 ppm borates for some more pH buffering.

[dlleno]

just a quick comment on my experience here. I have added 50ppm Borates via boric acid from Duda.. I started with 50ppm TA (made this adjustment first before adding the BA). the only surprise to me is that in order to keep pH rise under control I have to target a higher value (i.e. 7.6--7.8) and run with TA = 30ppm. yea thirty parts per million total alkalinity, which sounds a little scary. but I'm watching it carefully and so far so good. FYI my CA is 140. Water is still "young" in that I haven't yet switched to bleach

[chem geek]

Targeting a higher pH target is not unusual, but yes you need to be careful with your lower TA level. The borates and CYA will buffer the pH somewhat, but for preventing a drop in pH the TA is the stronger buffer (then CYA and the borates the least -- the borates are strongest when the pH gets higher). This chart shows that water is more over-carbonated at higher TA and lower pH.

Unless you are adding acidic sources of chemicals, your TA should not drop. Just be careful and check every now and then and note that Dichlor is net acidic so it WILL drop the TA. For every 10 ppm FC added by Dichlor, it lowers the TA by 3.5 ppm. Once you switch to using bleach, the TA should not drop unless you add acid which is unlikely given the tendency of the pH to rise.

You must have aeration jets on in the spa because your pH is apparently wanting to rise a lot even though you are add Dichlor which is net acidic.

[dlleno]

ok good; thanks. yes I'm adding net acidic things: dichlor itself, but won't the conversion to hypobromous acid via the bromide bank exert even a stronger downward pull onto pH? I keep the spa at 4-6ppm, but when away for several days the ozone generator is able to keep about 1 or 1.5 ppm bromine now. yay for ahh-some.

Since starting out at TA=50ppm I have added four teaspoons of dry acid to keep pH below 8.0. this drove my TA down to 30ppm or maybe 35 (granularity below increments of 10ppm is difficult). over the last 1-2 weeks my pH has settled down to 7.4, so I added a tablespoon of Soda, and that brought TA back up to 40ppm. hope this means I can start to build up TA to more comfortable levels.

yes my jets are many and all use air injection. I do have a full time ozone generator as well, so lots of aeration happening.

[chem geek]

When you add bleach the pH rises and this doesn't change just because it creates bromine.

NaOCl + H₂O + Br^- ---> HOBr + NaCl + OH^-

Bleach (sodium hypochlorite) + Water + Bromide Ion ---> Bromine (hypobromous acid) + Salt + Hydroxyl Ion

When the bromine gets used up oxidizing bather waste, this is an acidic process, just as it is when chlorine does the same thing:

3HOBr + 2NH₃ ---> N₂(g) + 3H⁺ + 3Br^- + 3H₂O

Bromine (hypobromous acid) + Ammonia ---> Nitrogen Gas + Hydrogen Ion + Bromide Ion + Water

The net effect of addition and consumption/usage of bromine is pH neutral.

Now if some of the bromine creates a combined bromine with an organic and doesn't get fully oxidized and instead either builds up or gets filtered out, then you can have a net pH and TA rise, but not a net drop.

As for ozone producing bromine, that has the same net effect as adding bleach to create more ozone in that it has the pH rise

O₃ + Br^- + H₂O ---> HOBr + OH^-

Ozone + Bromide Ion + Water ---> Bromine (hypobromous acid) + Hydroxyl Ion

so again when combined with the net acidic usage/consumption of bromine the overall effect is pH neutral.

[dlleno]

ok I'm going to have to ask some more questions to make sure I'm following. thank you for that in depth analysis!

What I get from the above is essentially:

"When you add bleach the pH rises"

BUT "oxidizing bather waste ... is an acidic process"

THEREFORE "The net effect of addition and consumption/usage of bromine is pH neutral"

However, "Dichlor is net acidic so it WILL drop the TA". why is this? is it because of the CYA?

Is it true, then, that the net effect of addition and consumption/usage of bromine is net acidic when dichlor is used as the oxidizer but pH neutral when bleach is used as the oxidizer?

Also I think you are calling out that the answer to this question:

(dlleno asked:) "I'm adding net acidic things: dichlor itself, but won't the conversion to hypobromous acid via the bromide bank exert even a stronger downward pull onto pH?"

is essentially this: No - when you add dichlor, the net pH effect is no different whether there is a bromide bank present or not"

Also help me understand the conventional spa store wisdom: Why do they tell us that hypobromous acid is a "stronger" acid than hypchlorous acid and therefore the use of bromine will be net acidic compared to chlorine?

[chem geek]

When you add Dichlor to the water it mostly does the following where "CY" is the CYA core ring where H₃CY would be Cyanuric Acid (CYA).

NaCl₂CY + 2H₂O ---> 2HOCl + H₂CY^- + Na⁺

Dichlor + Water ---> Chlorine (hypochlorous acid) + Cyanurate Ion + Sodium Ion

and then the chlorine oxidizes bromide to bromine:

HOCl + Br^- ---> HOBr + Cl^-

Chlorine (hypochlorous acie) + Bromide Ion ---> Bromine (hypobromous acid) + Chloride Ion

So the addition of Dichlor is not acidic -- it's close to pH neutral. It's the consumption/usage of chlorine or bromine that is acidic so combining the two steps makes this net acidic. So the way to look at it is that adding bleach makes the pH rise while the usage/consumption of the resulting bromine has the pH drop back down. When you add Dichlor, there's not much pH change but when the resulting bromine gets used up the pH drops. So I wouldn't characterize what is going on by saying that it's due to CYA being an acid. I would instead characterize it by saying that bleach is alkaline and Dichlor is close to pH neutral. So when you factor in the acidity of bromine usage/consumption, you want what you add to be alkaline if you want the net result to be pH neutral.

So you got the net effect correct. And yes, you also understood that the pH effect is independent of whether or not there is a bromide bank.

The conventional spa store saying that hypobromous acid is a stronger acid is not true at all -- it's actually a weaker acid which is why at spa pH it's mostly hypobromous acid while with chlorine at pH 7.5 it's 50/50 hypochlorous acid and hypochlorite ion (i.e. it's roughly half dissociated). The reason the conventional spa store says that the use of bromine is net acidic is that this is true when one uses bromine tabs since the bromine released from them is close to pH neutral but the consumption/usage of that bromine is net acidic. Bromine released from tabs is very similar to having chlorine added from Dichlor. Also, when making bromine from a bromide bank, spa stores generally recommend using Dichlor so that usage is also net acidic. If they recommend non-chlorine shock (MPS) then that is acidic upon addition so is even more net acidic. Since they don't recommend bleach, pretty much every usage of bromine is net acidic.

[dlleno]

thank you for that explanation its making more and more sense. Your explanation confirms what I am seeing now, which is that after a couple of weeks of dichlor as the oxidider my pH rise is no longer an issue and I'm back up the 50pm TA to keep the pH from falling. What you are implying is that once I switch over to bleach (which is due soon), the pH drop will become even less of an issue and I won't have to add as much soda over time.

So as a conclusion to my pH rise, which initially caused me to drop TA to 30ppm (due to heavy aeration): I would say this condition was quite temporary in the sense that after a few soaks and dichlor as the oxidizer things are stable now at more reasonable TA levels. Moreover, my ozone generator (after cleansing the spa with ahh-some) now is able to maintain a residual of about 1.5ppm bromine with no bather load and no added oxidizer. Basically I'm using a "two-step bromine, dichlor then switch to bleach, with borates" chemistry, which I may summarize in a separate post unless that would be redundant. things are going very well: My starting numbers were TA=50, CA=140.

[chem geek]

Yes, when you switch to using bleach you shouldn't see any more pH drop and the TA should become stable. If anything, you may see the pH rise and need to add some acid (but don't try and lower the pH below 7.5 and shoot instead for a target pH of around 7.7 or 7.8), but hopefully you won't have to add very much acid.