Baffling measurement changes - total hardness plummeting when adding bromine/shock.

[BobbleWobble]

Hi guys - I have a scientific background and fully read through the manual of both the chemicals I bought with the tub, and also the Taylor reagent kit I got to try to figure this out - and I still don't understand what's happening here (the fact that I'm red-green colorblind and all the measurements are color-based doesn't help). Any help would be very much appreciated:

I cleaned, drained, and refilled the hot tub (~300 gallons) a few days ago. Did the 7-in-1 (JNW brand from amazon) test strip reading and everything looked normal. Hardness ~160, alkalinity ~180, pH ~7.6. Good to go, right?

So I then added ~1.5 oz bromine booster (bottle says 0.5oz per 100 gallons) and ~1.5 oz shock (Potassium peroxymonosulfate, bottle recommends 2oz per 500 gallons), let the jets run for ~15 minutes, but a few bromine tabs in the floater, and covered it for the night

This afternoon, I opened it up and there was a somewhat strong chemical odor. Did the 7-in-1 strip and two things immediately jumped out: (1) the hardness dropped off the map. The scale is supposed to go from green to dark green but the strip was almost yellow, and (2) the bromine reading was still basically at 0 ppm, despite the bromine (?) smell.

The alkalinity and pH were essentially unchanged. I re-did the test with two more strips and saw the same thing.

I hope this is obvious and I'm just dumb, but I don't understand why after adding bromine and shocking, the hardness reading would plummet yet the bromine would be unchanged.

Also I read Waterbear's 3-step bromine guide just now and plan on following that, my only question is - his suggested TA (50-70ppm) seems a lot lower than the 'recommended' range in the other guides/test strips I've seen (usually 120-180ppm).  Is that difference crucial?

[waterbear]

19 hours ago, BobbleWobble said:

the fact that I'm red-green colorblind and all the measurements are color-based doesn't help

Which Taylor test kit did you get? The K-2006 and K-2106 are the recommended ones since the FAS-DPD sanitizer test is far superor and easier to read to DPD based testing. As far as the TA test, it is a color change from green to red in the Taylor kits so if you are having trouble with it have someone else read it. pH and CH measurements are based on other color chagnes so you should not have problems.

 

19 hours ago, BobbleWobble said:

Did the 7-in-1 (JNW brand from amazon) test strip reading and everything looked normal. Hardness ~160, alkalinity ~180, pH ~7.6. Good to go, right?

no, alkalinity is way too high and strips only measure total hardness, not calcium harness. Total hardness is a useless reading. Also, strips do not have the resolution to effectively balance water. The range is often too wide for even a "ballpark" guess as to the actual levels.

19 hours ago, BobbleWobble said:

(1) the hardness dropped off the map. The scale is supposed to go from green to dark green but the strip was almost yellow, and (2) the bromine reading was still basically at 0 ppm, despite the bromine (?) smell.

Your hardness test and sanitizer test both bleached out because of high sanitizer and MPS. If you have the taylor K-2006 or K-2106m you would be able to get an accurate reading. IF you are using MPS (why? it's not normally needed!) then you need to also get the Taylor K-2941 or K02042 MPS interference remover add on kit for accurate readings. MPS will test as chlorine or bromine.

 

19 hours ago, BobbleWobble said:

his suggested TA (50-70ppm) seems a lot lower than the 'recommended' range in the other guides/test strips I've seen (usually 120-180ppm).  Is that difference crucial?

Yes, if you want good pH stability. Read these to help you understand the effect of high TA on pH. The second one will explain what is going on and will also show you the ONLY way to lower TA and keep it low.

https://www.poolspaforum.com/forum/index.php?/topic/52522-some-truths-about-ph-and-ta/

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

[BobbleWobble]

Thanks Waterbear! 

[BobbleWobble]

Sorry posted too fast and can't edit until the comment is approved so I'll just self-reply

Yep, I'm using the K-2106. MPS came with the chemical kit bundled with the purchase but I've read your 3-step bromine guide and am switching to bleach shock - also because my hot tub has an ozonator and apparently there are health risks of bromine + ozonator + MPS (https://www.canada.ca/en/health-canada/services/consumer-product-safety/reports-publications/pesticides-pest-management/decisions-updates/reevaluation-decision/2018/sodium-bromide.html).  Any thoughts on that?  I've only had the tub a while and it's outside and maybe used it a dozen times to hopefully the exposure to any harmful byproducts was minimal.

I think the consistently low bromine levels might also be due to some biofilm buildup in the pipes so I'm doing a Ahh-Some/drain/refill tomorrow and the TA of my water seems to be ~150 so I'll try to get it down a bit before correcting pH and then NaBr+bleach+tablets.  Thanks again for your help!