Can anyone explain why my test for alkalinity is turning yellow instead of red when I add the sulfuric acid? It works fine for my pool, but it does this when testing my fresh filled spa.
Adding sulfuric acid to test for alkalinity turns test yellow, not red
- Thread starter jkarn
- Start date
This is exactly it. Going to test again using the extra drop
It is really high; above the color chart. I used Bromine last year, did a full drain and refill this year to use Cl. I honestly don't know if the opening company put any chlorine in yesterday. However, its been doing this since immediately after the fill. The Ph was very high as well until today when I finally reduced that into a good range with Dry acid. In fact, the chlorine test was bleaching out as well as I would add the second reagent, and it would all be purple, then a quick flip of the testing vial and it went clear. That is, until this last test which is staying dark purple, but still above what I can discern. The latest alkalinity test was still bleached even after 4 drops of the first reagent. Though, the green solution was more green than blue this time. However, I still get yellow after 10 drops. No red. NOTE: I ordered my TFP Test Kit today.
- Jan 7, 2012
- 1,917
- Pool Size
- 21000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Use muriatic acid, not dry acid. You don't want sulfates in your water.
It turns out that there was probably still bromine left in the hot tub from the previous year. I took a water sample to Leslie's and they inadvertently ran the test for Bromine as that's what they had in the system of record. It was at 29ppm. When we added liquid chlorine, it oxidized and activated the reserve (that's my hypothesis anyway). For now, I'll wait for that to dissipate in the sun and heat and continue with Bromine. Next time I drain and refill, I guess I'll have to do a thorough rinse of the system.
- Mar 5, 2020
- 3,221
- Pool Size
- 66000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Astral Viron V35
I'm not sure how they did that, there is no test available (outside an actual lab) that could distinguish chemically between chlorine and bromine.
They would have just ticked a box "bromine spa" in their computer program and then it interprets the test results as bromine and makes them a factor of 2.25 higher than if they had ticked "chlorine spa".
When adding chlorine to a spa that contains bromide, then each mole of chlorine will turn 1 mole of bromide into bromine. When using weight based units then this turns into each ppm of chlorine (where ppm actually means the amount of FC that you would get from adding 1 mg Cl2 per litre of water) turns 2.25ppm of of bromide into bromine (ppm meaning now mg Br2 per litre). This factor simply comes from bromine being 2.25 heavier than chlorine on a molecular level. When counting molecules, then it's a 1:1 conversion between chlorine and bromine, when looking at weights, then it's a 1:2.25 conversion.
Whether you call that test result 29ppm bromine or 13ppm chlorine is just a question of the option they tick, doesn't mean there actually was bromine.
If no one has added bromide to the spa since your drain/refill, then there shouldn't be bromine/bromide in it now.
Ah, thank you for the explanation! That makes sense and they didn't explain this to me. Since it is still relatively cold here at night (40s), it's been cloudy, and the heat is still off... It may just be that the shock hasn't effectively burned off? Everything else on that test came back in a good range. Can I trust those results with the high sanitizer levels since it's a different method vs drops?
- Mar 5, 2020
- 3,221
- Pool Size
- 66000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Astral Viron V35
- Mar 5, 2020
- 3,221
- Pool Size
- 66000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Astral Viron V35
Please don't meddle with trying to lower pH while your pH test is still affected by high chlorine. If the TA indicator is still affected, then the phenol red must be too.
High chlorine turns phenol red into chlorophenol red, which still is a pH sensitive dye, but changes colour over a lower pH range:
At normal pool pH, chlorophenol red looks purple, making pH look high.
If your pH now looks "normal" despite high FC after adding acid, then it might actually be quite low now.
The TA indicator is a mixture of Bromocresol Green and Methyl Red:
High FC bleached out the Methyl Red leaving behind the Bromocresol Green. If the TA test starts out looking more greenish than blue now, then this is another indicator that your pH is now quite low.
I am starting to wonder if the best option would be now to drain the spa and start new.
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Being told your chlorine is actually bromine is a new one to add to the "stay out of the pool store" list...
Add another vote for "drain it", if the pH has crashed and the FC is high then the water is not doing anything good to your tub or equipment.
Add another vote for "drain it", if the pH has crashed and the FC is high then the water is not doing anything good to your tub or equipment.
Thanks everyone! For the record, I wasn't told it was bromine, it's just that they ran the test as bromine because that's what I had in their system. Gonna test again when I get a chance and then, if the levels of sanitizer (assuming now it was just chlorine shock and I'm overthinking residual bromine) haven't come down I'll drain and refill.
I wanted to send an update. It turns out that overnight, the sanitizer levels dropped. I found that the pool guys shocked it, and I wasn't aware as I only have them open the pool and usually manage my own chemicals throughout the season. Once the levels dropped, I was able to get an accurate reading and everything is now balanced.