Alkalinity Moved FAST

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I am eager to learn because I am an advanced aquarist and I have perfectly balanced aquariums (at least what we consider balanced in the aquarium world) so I have some knowledge in water chemistry to build off.

Bubble tubs should aerate just as much as jets imo, instead of turning the surface with oxygen your injecting it directly into the tub, bubbles have a lot of surface area to absorb oxygen into the water as they rise and shrink I would think. I have to get this under control because constant use of sodium bisulfate scares me....where is all this sodium bisulfate going after it is used? Does it gas off or stay in the water raising the TDS?

I tested my tap water it comes in at 200ppm of CH. I will just roll with that no need to lower or raise it.

Thanks for your CSI write up, can I ask if the CSI has anything to do with your health or comfort? Or is that just for the tub and equipment? I am a perfectionist at heart so of course I am fighting for "0" but is this extra stress really necessary?

One other thing I wanted to mention, after about a week of using it daily with liquid chlorine I noticed my CYA just barely move to potentially below 30ppm so I had to chlorinate it once more using dichlor. Should the CYA be dropping? I may need to use dichlor in place of liquid chlorine once a week or so. The tub water gets no sun light to speak of.
 
The hydrogen in the sodium bisulfate (NaHSO4) eventually becomes water. The sodium and the sulfate probably stay as ions, increasing TDS. Here's why aeration raises pH:
1. Aeration causes CO2 to outgas. CO2 (aq)->CO2 (gas)

2. Carbonic acid (H2CO3) in the water then creates CO2 according to this reaction: H2CO3 ->CO2 + H2O

3. Bicarbonate (HCO3–) in the water creates carbonic acid (H2CO3) according to this: HCO3– + H+->H2CO3

​
Net result: H+ is consumed and pH goes up — alkalinity does not increase
​
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TDS will increase with muriatic acid, should you use that instead of sodium bisulfate. In that case, you add chloride ions to the water instead of sulfate ions, since the hydrogen is consumed (HCl). You add TDS when you add bleach. You add TDS when you add anything.

Don't worry about it though, you dump the water every 3-6 months in a spa, long long before the TDS gets anywhere high enough to matter. Heck, the guys running SWG add 3000-4000 ppm of salt right off the bat, so what builds up from adding a bit of acid or bleach doesn't matter.
 
Thanks for the explanation :)

Should I or is there any benefit to using liquid muriatic acid over sodium bisulfate? I know it is more dangerous to handle and the manual says not to use it in the tub. I have a gallon of it on hand for my pool though, may be cheaper in long run than buying sodium bisulfate?

I drained my tub this morning and refilled using 100% unsoftened tap water. The test results after refill were the following:
CYA: 0
CH: 190
TA: 60
pH: 8+ (unknown)
FC: 0


So I took the following actions and am awaiting results:
CYA: +1oz cyanuric acid
CH: None
TA: None
pH: +1oz sodium bisulfate
FC: +1oz of 10.5% liquid chlorine

*all ounce measurements are by measuring cup volume not weight.


- Is it necessary to wait after raising TA before adjusting pH?
- Is 10.5% an odd percent for liquid chlorine from Pinch-a-Penny?
 
I tested it after 12 hours and my new results followed as:
CYA: 20
CH: 190
TA: 40
pH: 7.4
FC: 0.5


So I took the following actions and then used the tub an hour later:
CYA: +2.5tsp cyanuric acid
CH: None
TA: None
pH: None
FC: +3.5tsp of 10.5% liquid chlorine


I wanted to see what 40ppm of TA would do to my pH of 7.4 after an hour of use today and the results were that the TA did not drop any further and the pH only rose by 0.2 to a total of 7.6

According to PoolMath my TA of 40 throws the CSI off too much to -0.53 but a TA of 50 like stated here brings me into -0.39 so I am raising my TA back to 50. Somehow it dropped from the 60ppm tap level.


As of writing this post a few hours after using the spa today here are my test results:
CYA: 45
CH: 190
TA: 40-45
pH: 7.6
FC: 0.5


So I took the following actions and am awaiting results:
CYA: None
CH: None
TA: +2tsp baking soda
pH: +0.5tsp sodium bisulfate
FC: +1oz of 10.5% liquid chlorine
 
pinkfloydeffect said:
According to PoolMath my TA of 40 throws the CSI off too much to -0.53 but a TA of 50 like stated here brings me into -0.39 so I am raising my TA back to 50. Somehow it dropped from the 60ppm tap level.
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Not somehow. You added acid (sodium bisulfate) to lower your pH. It dropped your TA as well, because that's what it does.

As the others have said, move slowly. I especially would recommend not trying to adjust both TA and pH at the same time, since they are interrelated. Let it sit, see where it's at, leave it be if it's good.

Also, your CSI of -0.53 fell within the range TFP considers to be acceptable, so you could have left it there. I accidentally overshot my TA reduction to 40, I would have left it except for my water my pH dropped below 7, so I raised it back up to 50.
 
Should I buy more sodium bisulfate dry acid when I run out or start using liquid muriatic acid?

Thanks for the advice everyone, curious what adjusting my TA would have done to the pH of 7.6 I will wait next time.

I am about to get back in the spa for the night, so here are my latest test results:
TA: 50
pH: 7.5


So my TA is back where it was @ 50ppm and the sodium bisulfate compensated the TA rise. So I will let the pH drift until it hits 8.0 then work with the sodium bisulfate again. However that will lower the TA again and the cycle goes around...seems like IF I hit 8.0 I will need to raise TA before adding sodium bisulfate acid again right? There must be a formula so I know how many ppm over my target I need to raise the TA to before adding X amount of acid.
 
Muriatic acid is preferred over sodium bisulfate. The sulfates will destroy the heater in your spa.

Please also quit being so concerned about CSI in a spa. It rarely, and I mean rarely, has any effect on a spa, especially fiberglass.

Take care.
 

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Does your fill water have metals in it? Have you had the water tested for that? Were do you live? Can you add your location to your settings?
 
the slightly higher ph will raise your csi if that is your main concern
leave your ta alone and dont worry about it unless you start to get wild ph swings
when lowering your ph aim to go from 8 to 7.8
you will find a sweet spot, my pool is now at ta 50 and ph 7.6 and i havent had to add acid since july
 
mknauss said:
Does your fill water have metals in it? Have you had the water tested for that? Were do you live? Can you add your location to your settings?
Click to expand...

Not sure I have not tested, but have been told it is bad. I live within New Port Richey, Florida.

aussieta said:
the slightly higher ph will raise your csi if that is your main concern
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Comfortable pH for sensitive skin is my main concern.
 
I used to be able to keep my pH stable for about 7-8 uses before needing acid, now I need it before every use so something is not right. I started with an alkalinity of 50ppm and somehow maybe through top offs it has risen to 80ppm. It only takes less than an hour in the spa to get burned when the pH is 8+ as soon as my skin dries off I feel sun burnt. So should I drop my pH to 7 with acid then aerate back up, and that should give me a stable Ph again for a while?? I am hoping that will also drop the alkalinity back down to 50.

To answer the question above, my tap pH is 7.2-7.3

Regarding FC to CYA relationship, that sounds like it can be a nightmare. My spa always sits around 40ppm CYA, but the FC fluctuates from 2-6ppm. It gets consumed so fast using liquid chlorine that there is never a steady FC just a window of 2-6. I just tested my CYA because it has been a few weeks and it is below 30ppm so I need to raise that, this could explain the chlorine consumption but I do not think it is pH & ALK related right?? I made the relation between burnt skin and pH, I am willing to bet even with a low CYA right now I could use it with a lower pH and not get burned at all.
 
Top offs will affect the ph and ak depending on the levels of your fill water. I noticed had this issue so I now add a small amount of acid at top off to account for this. You have to experiment a little to arrive at the right amount of acid. Remember that aeration will affect the ph, so wait until you've ran the air jets for about 1/2 hour before you take a new reading.
 
Seeing how my tap pH is 7.2 I can not see how adding that would raise the pH. On the other hand it will raise the alkalinity, but adding acid will not help me during top offs unless I am adding enough to lower the entire spa to 7.0-7.2 to reduce the alkalinity. The problem is there is no way to lower the alkalinity of top off water unless I was to fill a 5 gallon bucket and then lower the pH to 7.0-7.2 in the bucket before adding it...but since my tap is already 7.2 to begin with I am not sure this would work either.
 

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