Dry Acid Causing Yellow Water?

[G-Dub]

Just installed a new marquis 350 gallon spa. Using a Taylor test kit, and the floating mineral + bromine spa frog, plus a bromine reserve added initially. On start up after first fill while balancing water I noticed yellow discoloration to the water and a yellow stain on the water line. I then noticed when I was adding dry acid to lower alkalinity the when the powder hit the water it immediately turned yellow. I tried putting some spa water into a bucket and adding the acid to that, same result. I'm reasonably sure this is where the yellow stain is coming from. Never seen this before, has anyone else experienced this? Is this something to worry about? My ph was 8., TA staring was 180, CH was 70, I had also added calcium up, the bromine reserve and bleach as the shock, along with the ph down. I'm now up to CH of 150, TA 80, pH still 8.0 so was adding a bit more ph down to bring the TA down to 60 or so. Bromine levels about 12, I haven't put the spa frog in yet.

Thanks!

[Dr. Spa]

Are you on well water?

[waterbear]

very possibly you are converting the bromine into elemental bromine because of low pH (NOT a good thing!) Which taylor kit are you using? If you are NOT using either K-2006 or K-2106 then your bromine reading is suspect and is possibly much higher than 12 ppm which would cause your pH to read high when it is not becaus of a chemical interference between the bromine and the phenol red indicator. This would mean tha the pH is not as high as you think it is and you have dropped it low enough to cause the hypobromous acid to convert to elemental bromine in the water. Why are you going with a spa frog? It will add metals to your water and really will NOT allow you to run lower bromine levels under real life conditions!

Well water can contain iron that can color the water yellow and cause stains but adding dry acid usually will lift the stain, not make them more apparent. You might have a combination of things going on here since you said that the water was yellow when you filled and you have stains (this could be iron) but the dry acid effect and the fact that you have put in a lot to lower TA (did you do an acid demand test to determine how much to add to lower the pH to 7.0 and not lower) makes me suspect that you have formed elemental bromine. Had you already added any bromine or sodum bromide when you first noticed the yellow color or was it when you filled the psa before adding any chemicals?

Here are instructions to safely lower TA.

[G-Dub]

Thanks for the advice. I am using the K-2006 kit although purchased the 0872 reagant when I switched from chlorine to bromine (on my last spa).

So I tested my water out of the tap before adding any chemicals, using the drop kit I found CH 70, TA 180, pH 8.0.

After filling the tub completely I tested again, before adding any chemicals, and got the same results.

I then added calcium up, bromine reserve (per directions on bottle) and bleach shock (one cup) all at once. I knew I would need to lower my TA considerably (about 100) so I added 2oz of ph down and aerated, pH was 7.4, TA was 150, did it again, pH 7.8, TA 120, did it again, pH 7.4, TA 80. This morning TA was 80 but pH had crept to 8.0 so I added another 2oz of pH down (total of 8oz so far). Each time I added pH down I noticed immediate yellow cloud in the water upon adding....

Not well water, this is tap water and filled through a hose end filter. 350 gallon spa.

I thought I would try the spa frog but definitely not convinced. i was happy using a bromine floater before and likely will go back to that, especially if you guys recommend it...

[waterbear]

Are you using the acid demand test to determine how much dry acid to add to lower the pH 7.0 and not lower? As you lower the TA you will need less and less acid to achieve the pH drop to 7.0.

Adding about 1 oz of dry acid by volume or 1.5 oz of dry acid by weight would drop the pH in a 350 gallon spa from about 8.0 to 7.0 when the TA is at 80 ppm but when the TA is 180 ppm you would need more than double those amounts for the same pH drop! Adding 2 oz each time (you did not say if it was by weight or volume) would get your pH dangerously low. Your test kit has an acid demand test. This is what it is used for!

I would have started with lowering the TA first and then added the bromine and bleach since it does not take that long to lower TA in a spa because of the amount of aeration you can get easily.

It really sounds like elemental bromine to me, which is toxic and occurs when the pH is extremely low. Adding the dry acid undissolved will create pockets of extremely low pH but they should dissipate quickly as the water circulates. If all the water stays yellow then you added too much acid. You might want to predissolve the acid and add it slowly around the perimeter of the spa with the circulaton running.

[G-Dub]

OK gotcha. Now I have the TA and PH in reasonable range and the water seems clear, I cleaned the water line and mostly removed the yellow color. Should the spa be safe? I take it the elemental bromine will convert back when in a reasonable ph range. Or do I need to drain and refill, this time balancing the water before adding bromine?

[HottubJim]

On 9/5/2012 at 6:10 PM, waterbear said:

Adding the dry acid undissolved will create pockets of extremely low pH but they should dissipate quickly as the water circulates.

You might want to predissolve the acid and add it slowly around the perimeter of the spa with the circulaton running.

Hi Waterbear, first off, Merry Christmas! I've been a long time lurker on these forums and you (and a couple of others) have saved my bacon time after time with the knowledge you share.

My question is about adding dry acid (as pH-) into my hottub. I really don't like pre-dissolving in a bucket, as my ground can be super slippery (plus stairs down to tub etc) and it worries me that I'll spill the highly acidic solution on myself/the dog/plants! SO I really would prefer to dose directly into the tub, but I've always been dissuaded from doing so by reading bottles, reading forums & listening to hottub store advisors.

From your quote above I understand that in a hotub it is probably OKAY to add the dry acid directly into the tub (due to the inherently good circulation). Using this method, would you advise dosing the dry acid around the perimeter presumably, and how long would you leave the blowers on to help it dissipate before testing/using and would you test from the centre of the footwell for instance for certainty of dissipation, or shouldn't it matter?

Thanks so much and apologies for bringing this old thread back from the 2012 dead!

[waterbear]

On 9/5/2012 at 1:10 PM, waterbear said:

Adding the dry acid undissolved will create pockets of extremely low pH but they should dissipate quickly as the water circulates.

On 9/5/2012 at 1:10 PM, waterbear said:

You might want to predissolve the acid and add it slowly around the perimeter of the spa with the circulation running.

 

Why not just carry the bucket of water to the tub or use a hose to fill the bucket at the spa (I know you have to have a hose that reaches the spa or you cant top off the water or do water changes), dissolve the sodium bisulfate into the water (a large plastic bucket is best and stir with a plastic or wooden spoon with no metal parts) and then pour it into the tub with the circulation running. Dry acid should always be predissolved  before adding it to  a tub and added with the circulation on. Period. End of Story! The pellets take a while to to dissolve and can cause damage since they create pockets of very low pH if added directly to the water.

Fun fact, when dry acid is dissolved or touches a moist or wet surface it forms hydronium ions, sulfate ions,  and sodium ions, this is basically what happens when sulfuric acid is added to water but there is no sodium ions present. Another way of looking at it would be that you are forming a mixture of sulfuric acid and sodium sulfate in the water since dissolving sulfuric acid in water will form HSO4- + H3O+ ,  and sodium sulfate would form Na+ + SO42 and the net ionic species that would form would still be sodium, sulfate, and hydronium.

NaHSO4 + H2O --> Na+ + HSO4- + H2O
Na+ + HSO4- + H2O <-> Na+ + SO42- + H3O+

One final note:

ALWAYS ADD ACID TO WATER AND NOT THE OTHER WAY AROUND when diluting or dissolving! Adding acid to to water produces heat (exothermic reaction) and if you add the water to the acid, whether liquid or dry acid, the heat generated could cause the water to boil and splatter acid out of the bucket. Adding the acid to the water slowly prevents this.

Fun Fact: the crystal toilet bowl cleaners Vanish and Sani-Flush (both discontinued in 2009) were mostly sodium bisulfate with fragrance and detergent added, which is why they were so efficient at removing scale from toilets.

[HottubJim]

1 hour ago, waterbear said:

Why not just carry the bucket of water to the tub or use a hose to fill the bucket at the spa

Even close to the tub, there's still a big bucket of very acidic water to hold at torso height to then distribute around the tub. One slip, and it's acid all over the torso. That's just my personal fear. Also, when stirring the solution to dissolve, there's an acid splash risk.  Surely this represents way more risk than necessary, when the tub's naturally gonna agitate the acid granules into solution pretty good (especially with a much bigger body of water)?

1 hour ago, waterbear said:

The pellets take a while to to dissolve and can cause damage since they create pockets of very low pH if added directly to the water.

Makes sense, but surely with the (relative to a pool) the heat and agitation of a hottub with blowers on, surely they should dissolve pretty quickly?

I guess my question for you (where user adds dry acid to the tub undissolved) is twofold:
 - Is the risk: (a) damage to hottub components or, (b) damage to bather due to a pocket of highly acidic water

and

- If the risk is to the bather, then assuming bather & chemical balancer is the same person: Which is the greater risk/ register of likelihoods?

Sorry for asking more questions, I am just trying to understand better.... Am I the only person paranoid about this issue 😅 ... I just hate having to regularly deal with a 5 litre bucket of extremely acidic solution. The weather where I am is regularly rainy, I have decking one side (which can get slippery as a result); steps; and on the other side loads of slick muddy grass (for half the year). 

[waterbear]

Don't mix it all at once. Do it in smaller batches that you can handle safely. If you can't walk it around the tub just pour it slowly directly in the the stream from a jet and it will disperse and mix quickly. If you want to add it directly to the tub be my guest but it is not the proper way to do it for many reasons such as the undissolved granules dropping and sitting on the surface of the tub or, even worse, being pulled into the drain when they are partially dissolved and can get though the strainer and into the pump and heater where they can cause more damage. I can't stop you from doing that, only advise against it but then again, what do I know about hot tubs, pools, and water chemistry? 

The solution is not that dangerous once mixed, the dry chemical is actually more dangerous if you get it on your skin, particularly if moisture is present.

You never said how big your spa is but in a 550 gal spa it only takes about 1 oz or 28 g by weight or 1.5 Tablespoons or 21 ml by volume of dry acid dissolved in a bucket of water to lower the pH from 7.8 to 7.6 (a good place to keep it) assuming a TA of around 40-50 ppm  If your spa is smaller the amount needed is even less. You are not handling a concentrated acid by any means once dissolved.

If you spill it on yourself just jump into the tub and then rinse off with a garden hose. When you dissolve it stir slowly so it does not splash, put a non slip mat on the deck where you are standing if the deck gets slippery, and pour it slowly from the bucket. It's common sense.

Final note, if you are afraid of the chemicals needed to balance your tub perhaps you shouldn't have a tub. Just sayin'.