Low pH, stable TA... what gives?

[bbrock]

Hi you all,
I am now questioning the pH in my spa. While I thought I would see this climb, like in the pool, it usually falls. I use the 3 step bromine system as outlined at this site. It was today that I did some reading and learned that the bromine tabs I keep in the floater are relatively acidic and will lead to a drop in the pH. I keep the water temp at approx 100. Here are the latest levels:
Br 10+
pH 7.1 (hard to decipher today. The color was slightly orange, slightly pink. I could not tell if it that was the color after 7.2 or leading to 7.2)
CH 150
TA 70

Now, I am not sure what to do to stablize the pH. I was thinking the TA of 70 wa keeping things stable, but I guess it has not been. I don't think I can get accurate tests w/ the pH tomorrow AM b/c I just shocked it this AM and that shoots the Br and pH way up. Once the Br falls to 10 or less, can I then get the pH level and assume it is relatively accurate?

Should I add baking soda to bring up the TA slightly? If I raise the TA to 80, will that help or make any difference?

Do I add soda ash or washing soda to bring the pH up? I was trying to look around the forum a little, and I didn't see this being done in spas.

Am I supposed to aerate instead of the soda ash or washing soda to bring up the pH?

Confused on how to proceed. Appreciate any help. Tx.

 

[chem geek]

When using net acidic chemicals, such as bromine tabs, you can raise the TA level so that there will be more carbon dioxide outgassing so the pH may be more stable. Note that the TA will still drop over time. You could increase aeration of the water as another alternative, but again this will not change having the TA drop over time from the acidic bromine tabs. Up to you which way you prefer. Probably increasing the TA would be the easiest. Just make sure your CH isn't too high since you don't want to have scaling in your spa.

At some point you can probably use pH Up to adjust pH and the rise in TA from that product will equal the drop in TA from the bromine tabs, but be careful to not have the TA too high. I'd keep the CSI no higher than -0.2 to prevent scaling in the gas heater.

 

[bbrock]

Tx Chem Geek.

Would raising the TA to 80 from 70 help out at all? How much would I want to raise it?

You recommend pH up (which is sodium carbonate, right?) vs. using borax? I think Pool School recommended either one. Just trying to figure out why one vs. the other... pros/cons. But, wouldn't Arm & Hammer Super Washing Soda be the same thing as a standard pH UP for that matter?

Pool Math shows that with my levels and criteria from above, at TA 70 balanced water can be maintained with a pH of 7.4-7.9. Whereas with a TA of 80, the pH range is 7.3-7.8. Now when u say keep no higher than -0.2 to prevent scaling, I see when the pH is more negative I'm at risk for plaster corrosion, but when pH is a + # I'm at risk of scaling. Perhaps I'm not following u when u say "keep CSI no higher than -0.2."
BTW, I cover the spa, if that matters.

 

[chem geek]

At the worst-case temperature of 104ºF and with 150 ppm CH (you didn't list your CH level and 120-150 ppm is typical to prevent foaming) and with a pH of 7.5 you'd get to a -0.2 CSI with a TA of 55 ppm. If your pH were to rise to 7.8, the CSI would be higher. If your CH were 120 ppm, then your TA could get to 70 ppm (again at pH 7.5). So you can see that you don't have a lot of leeway if your CH is in that 120-150 ppm range. If you don't experience foaming and can have the CH be lower, then you'd be able to have a higher TA. For example, with a 50 ppm CH you could have 120 ppm TA with a pH of 7.6 and still be OK.

PoolMath is more oriented towards pools with its suggestions for CSI. Spas tend to scale more readily. Whereas in a pool we don't see scale until at least a CSI of +0.7, a spa can get scale at a lower CSI, certainly I've seen it at +0.3 and in the gas heater it may occur even at +0.0 since the heater is around 30ºF hotter so has a CSI about 0.2 higher. The hotter water also causes such scaling to occur more rapidly. Also, pH can often shoot up higher due to the aeration in a spa. For all these reasons, it's safer to have the CSI on the slightly lower side of 0.

As for plaster corrosion, your spa is acrylic isn't it? You don't risk corrosion from a lower CSI since you have no plaster or grout materials to protect. Metal corrosion comes mostly from lower pH.

 

[bbrock]

Sorry about the delay. Tx for the input Chem Geek. I appreciate your help.

Yes it is acrylic. And yes, the CH is 150. Do you know roughly how low the pH has to be to be subjected to metal corrosion? I assume it would be pretty low.

 

[chem geek]

The corrosion rate should be very low if the pH stays above 7.5. Even above 7.0 it will be slow but the lower the pH the faster the corrosion rate.

Remember that you really can't form a thin layer of calcium carbonate to prevent corrosion that easily so I wouldn't worry about that aspect at all. Just make sure your pH doesn't get too low and in a spa that's unlikely to happen given all the aeration (unless you use an acidic source of chlorine such as Dichor and don't run your spa jets).

 

[bbrock]

Even with a low pH, wouldn't metal corrosion be averted as long as I keep balanced water per Pool Math, or a CSI in the negative range as u suggested Chem Geek?

 

[chem geek]

Not if the pH were very low. A balanced CSI does NOT prevent metal corrosion. CSI is solely a measure of saturating the water with calcium carbonate. That is to prevent plaster and grout surfaces from dissolving and, at the other extreme, to prevent scaling. This link is to a discussion among corrosion experts explaining that the saturation indices are NOT corrosion indices. When the pool and spa industry talk about the saturation index being negative increasing risk of corrosion, they should say it increases the risk of dissolving/pitting plaster and grout surfaces and they should not say anything about metal corrosion.

Now, that said, the Recommended Levels (for pools) on this forum for pH all start at 7.5 so are at very low risk of metal corrosion. Now in your situation you are using net acidic chemicals, namely bromine tabs, and you say your pH tends to drop. To counteract that you can have a higher TA level but then would need to have a lower CH to prevent potential scaling. Remember that aeration can increase the rate of pH rise (or slow down the drop in your case) so if you believe that your pH is not at risk of climbing, then see if you can target a pH of 7.5. At that pH and even with 150 ppm CH to prevent foaming you could readily have the TA be at 80 ppm with a CSI of -0.2 at a temperature of 104ºF. Even a TA of 100 ppm would be a CSI of -0.1 and still be OK especially since your water isn't at 104ºF all the time. If you need your TA higher than that, say to 120 ppm, then I'd have your CH lower at 120 ppm. I doubt that you would need a higher TA than that even using bromine tabs.

Just keep in mind that even with a higher TA level to have the pH more stable when using bromine tabs, the TA will still drop slowly over time from use of the tabs. Every 10 ppm bromine that is used/consumed will lower the TA by 3.1 ppm. So you would need to use baking soda on occasion to maintain the TA level (or if you use pH Up because the pH still drops, then that also increases TA).

 

[bbrock]

Tx Chem Geek.

You had mentioned to use TH up in order to raise the pH which would subsequently raise the TA, but yet the TA would get canceled out by the acidity of the bromine tabs. Why would I want to do that when I can have more control over the TA by just separating the two and using borax to raise pH, and baking soda to raise TA?

 

[chem geek]

The bromine tabs are acidic when the bromine is used/consumed and that will lower both pH and TA. If you were to use borax or a pure base to raise the pH, then the TA would drop over time. Using pH Up will add both but you are right that if you wanted to you could control them separately. You would add Borax to compensate for the acidity of the bromine tabs (including the bromine usage/consumption) and you would add baking soda to compensate for the carbon dioxide outgassing. I was just assuming that there was a sweet spot TA level where adding pH Up (same as Arm & Hammer Super Washing Soda) would compensate for both with a single chemical. It's up to you if you want to have more control with two separate chemicals. That would let you have a lower TA level if you want to lessen the amount of baking soda you need to add.

 

[bbrock]

I'm not sure what the ideal "sweet spot TA" would be. That is the problem. All I know is the the pH drops and the TA seems to be holding relatively stable. I need to check it for this week. Last week it was 70. Perhaps if I raise it to 90, with my CH of 150 as shown from last week, that would be better. I could still have balanced water per the CSI scale, and try to heed what you are saying about keeping the CSI on the negative side from 0 to -0.20. I guess I am just wondering if raising the TA to 90 will keep the pH from dropping so much/fast.

The problem I have/fear with adding Arm & Hammer Washing Soda is that it will raise both the TA and pH, and perhaps it will shoot the TA too high and for too long. It doesn't seem like the acidity in the bromine tabs or shocking with bleach affect the TA and lower it. As such, I have a feeling that I could get into more of a problem w/ the Washing Soda.

But, on the flip side, looking at the borax I now have other concerns. I researched about borax and the health effects. It appears that it is an endocrine disruptor and negatively impacts the reproductive system. Yes, I know that too much hot water in general may affect a male's reproductive system, and I won't be letting my twins use the spa until they are much older or I keep the water cooler, but I now don't feel comfortable adding borax if it could cause these things. Any input from all the chemists out there on this?

At the same time of all this, I actually wash researching making my own dishwashing powder detergent, and it had called for 1/2 part borax to 1/2 part baking soda. But, after having read this about the negative health effects, I have held off. I don't want to use anything in the dishwasher that could leave a residue, however miniscule, on our dishware and affect our twins.

 

[chem geek]

I hear you. It sounds like you've got a better situation with the lower TA and just using Borax to compensate for the pH.

As for borax, or more specifically boron, and health effects, read Are Borates Safe to Use? Basically since you aren't drinking the water the answer to safety is yes because they are not volatile and have virtually no skin absorption (except through severely damaged skin). Also, the concentration is low so that you'd have to drink a huge amount every day for it to be a problem. Boron is normally found in the environment and your body excretes it so the issue is if you take in too much beyond what your body can handle.

However, where did you read that it was an endocrine disruptor? I can't find anything saying that. The EPA thinks that it probably isn't and the EC doesn't indicate that either. At higher levels it is known to affect testosterone levels in rats and testicle size in dogs and at much higher doses it has maternal effects so is classified as "probably toxic to reproduction" by the EC. However, the greater sensitivity is the Lowest Adverse Effect Level of 29 mg Boron/kilogram/day regarding male dog testes while the developmental issues in pregnant females is only seen at much higher doses where no adverse effects were seen at even 94.2 mg B/kg/day.

So the EPA starts with the No Adverse Effect Level from any of the studies and that is 8.8 mg B/kg/day. With 50 ppm Borates in the water, a 20 kg (44 pound) child would have to drink 3-1/2 liters of water every day and still be at the level where no adverse effects are seen. However, for regulation purposes, the EPA uses a factor of 10 safety margin for inter-species and another factor of 10 for intra-species so that would be drinking 35 ml or 1.2 fluid ounces per day. That's why the EPA allows up to 50 ppm Borates for such products in pools and spas.

If you don't want to use borates, then a pure base you could use would be sodium hydroxide aka lye. It's messy stuff, but it's used in making soap and readily available online. It usually comes in pellets, not powder, and it's very hygroscopic (absorbs moisture from the air).

 

[bbrock]

Very impressive Chem Geek. Tx for providing that info. That and ur link help to set the record straight.

 

[bbrock]

Reading through this again Chem Geek & looking at my levels this morning, I think I'm just going to try the pH up. When I look at the amount of pH up to use per Pool Math, it is such a trivial amount. 2 teaspoons (0.4 oz) to bring up the pH to 7.5 from 7.2. Because reading pH is a little challenging, I may just add 1 tsp (0.2oz) as my pH maybe 7.3; hard to read if it's going more orange or if it's light pink. Not to mention, the TA increase from the pH up will not be that significant and it will be eventually compensated by the acidity in the bromine tabs. Plus, it'll bring up my TA from 80 towards 90, and perhaps that will help to stabilize the pH drop.

 

[chem geek]

No, the acidity in the bromine tabs will only compensate for the pure base portion of pH Up. There is additional TA from the carbonate that is not compensated by the bromine tabs. Basically, pH Up (sodium carbonate) is identical to adding a pure base of lye (sodium hydroxide) and baking soda (sodium bicarbonate). The acidity of the bromine tabs is balanced by lye, but you are still left with the baking soda effect. Only aeration/outgassing will get rid of that added carbon dioxide from the carbonates.

However, since you are experiencing the pH dropping having the TA higher should be fine so go ahead and see how it goes.

 

[bbrock]

I raised my TA to 100, but only realized that with my latest CH of 400, I couldn't get the numbers to work on Pool Math. Kept leading to a high CSI w/ potential to get scaling. Latest spa levels:
BR 6
pH 7.2
TA 60
CH 400
Temp 100

I lowered TA to 60, but at the same time I have learned that if I leave the spa jets open so they blow air, I could drastically slow the pH drop from the BR tabs. Since my CH is a little higher, I figured I would lower the TA to help out the CSI and try to keep it slightly negative per Chem Geek's recommendation.

The problem is that I can't raise the pH from 7.2. When I took out the BR floater and added acid to lower the pH to 7.0 in order to lower the TA from 100, the pH did respond to the aeration and climbed back up. Hence I was able to repeat the process since the TA the first time dropped to 80. I tried lowering the TA again a couple days ago to get me to 60, and while I have the TA there now, the pH won't respond to my aeration attempts, and this is even without the BR floater in the water.

Here r the questions;
1. My CSI is negative and balanced now, but pH is 7.2. Is this ok?
2. If you see my other thread, "Spa heater needs replacement. What caused the failure?," you see a pic I posted showing the corrosion on my heater elements. If I am keeping balanced water, but on the acidic side, will this be a problem for my components? U say to keep the CSI lower Chem Geek, but I am concerned this lead to or exacerbated corrosion.
3. While it will increase my CSI to potentially cause scaling, should I raise my pH with borax, &/or raise my TA back up?

 

[chem geek]

You only lower your TA if your pH tends to rise. If your pH tends to drop or stay low, then you don't need to lower the TA (unless the CSI is too high).

The CSI shouldn't matter in your spa if there is no plaster or grout exposed to the water. Your use of bromine might be the reason since that is net acidic, though not as much as using non-chlorine shock (MPS).

As for metal corrosion, low pH is the most harmful. The calcium in the CSI won't stop that as much as keeping the pH higher. If you intend to keep with the same chemicals, then yes you could raise the TA and run jets to help raise the pH and maintain it.

 

[bbrock]

So far, I am periodically (about every 3 or so days) adding 2 tsp (0.33 oz) of borax to raise pH from 7.4 to 7.6. This seems to be good enough to bring the pH up for a few days, despite it falling d/t the acidic bromine tabs. Latest levels:
PH 7.4
BR 8-10
TA 80
Ch 400
Temp 100

I don't want to get the TA much higher b/c of my CH 400 and risking increased scaling but also foaming (I thought I read that high CH & TA could lead to foaming). Nor am I even sure if raising the TA to 90 from 80 would even slow the pH drop that much more. Note that in am earlier post I stated that having the spa jets open to aerate and waterfall on are helping to slow the rate of pH drop.

Here r my questions;
1. With adding borax like I am, even such a small amount, us this something that will accumulate and eventually have to start testing for? Note, I am just using borax to raise pH, rather than for water feel/characteristics?
2. How often r people topping off spa water? Yes I can expect evaporation d/t the heat, but the spa is covered and also not in the sun. Plus, it seems that since I have the aeration going now on the jets and waterfall on, I am seeing the water level drop a little quicker. Comments.

Tx.

 

[chem geek]

CH inhibits foaming and high CH and TA shouldn't cause foam, but you are right to be concerned about over-saturating the water with calcium carbonate since scaling is more likely in a spa due to the hot water temperatures. Your CSI is already +0.17 (from PoolMath).

Yes, the borax will accumulate borates, but 2 teaspoons in 300 gallons raises the borates by only 1 ppm so that's 10 ppm per month if you add this amount every 3 days. So after 5 months you would have 50 ppm borates accumulated and you'd likely be replacing the water before then unless you aren't using the spa very much at all.

Others will have to comment as to how frequently topping off is needed, but with the spa covered there should be little evaporation. So it's just evaporation when the spa is in use, though with jets on it's much faster.