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Wondering why TA and CH dropped suddenly


Matt16060936
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Hello, I'm a fairly new hot-tub owner, and have found tons of valuable resources on this forum. Now that I have a slightly complicated question, this was quickly my first-choice to seek guidance :) My tub is 425 gallons (Alps Spas Q-90), last cleaned and refilled on 1/22/17 (sodium bromide + floater + MPS), consistently tested with a Taylor K-2106 kit, and set to 102F.

Problem is my measurements today have me really scratching my head. TA dropped, and my CH plummeted. I've been busy so the tub's only seeing 1 or 2 bather-hours a week lately. Here's the last few measurement entries in my logbook:

2/11/17: pH=7.3, TA=120, CH=100, SI=-0.3, TB=0.5
2/12/17: pH=7.6, TA=130, CH=100, SI=0.1, TB=5
2/16/17: pH=7.6, TA=130, CH=90, SI=0.1, TB=4.5
2/20/17: pH=7.4, TA=90, CH=40, SI=-0.7, TB=5

Should I be worried that CH and TA tanked? I know bromine is acidic, which can lower pH and TA over time, but I've never seen my calcium dive like that.

Also, I did add Leisure Time "pH Balance" during this last refill, which says "Note: due to the unique buffering capacity of Leisure Time pH Balance, it is not necessary to adjust the calcium hardness level in your spa". Was that a mistake? Could it be interfering somehow?

Thanks in advance!

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I've thought about this a little more, and have a theory. Leisure Time "pH Balance" also says "pH Balance will soften hard water and precipitate calcium, resulting in cloudy water and/or a clogged filter". I have noticed evaporating water is starting to leave scale behind, so trying to increase CH when using "pH Balance" is a bad idea.

I found this post explaining how "pH Balance" is a phosphate buffer, how CH helps reduce foaming, how CH helps protect plaster/grout, and otherwise serves no purpose. Then I also found this post which explains how increasing CH is a bad idea when also using a phosphate buffer.

I think the solution to my problem is simply realizing I don't really have a problem: treatment and usage are going to affect pH, adequate TA will allow pH to remain level for a while, and CH doesn't matter since I have an acrylic shell hot tub (no plaster, no grout, etc). I also somehow got it in my head that keeping LSI between -0.3 and +0.5 would make the water more inviting because everything was balanced, but re-reading that part of my "Pool & Spa Water Chemistry" manual that came with the K-2106 reveals that's not true: a balanced LSI is for preventing scale or damaging concrete/metal.

So to resolve my minor scale issue I'm going to replace some treated-water with hose-water every now and then until scaling stops, and not care about my CH until this phosphate-buffered water gets replaced in a couple months. Also I probably won't use "pH Balance" any more, in favor of relying on a proper TA to prevent pH drift between checks/adjustments.

I hope I haven't introduced any misinformation, someone definitely correct me if that's the case because I've owned a hot tub for a total of about 5 months now :)

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