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Bromine levels keep dropping to zero

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Hey folks. I used to have a Freeflow tub, and recently disposed of it (multiple inacessible leaks). Anyhow, I located a free, used Strong Spa which had no pump or heater, so I was able to use my relatively new heater and pump setup from the Freeflow in this one. The former owners said the tub sat in their garage, on edge, for the last 6 months... so likely not very damp inside at all.

Long story short, the 'new'/used spa is 250 gal / 1000L. It looks very clean, and I filled it with ~250 gal fresh water, used Waterbear's method (TA to 100-110, pH to 7.6, add calcium, add sodium bromide (50g which per the package pre-treats 1000L of water), then shock with bleach (4% sodium hypochlorite = 1.33 cups, if I remember correctly).

The bromine levels shot up to shock levels. I have a Taylor kit but it's got the colour comparator for bromine... not counting drops. The levels were what I would expect for a freshly-shocked tub - above the 'high' and soon settled down to a perfect 'ok' (sorry, at work and cannot remember the actual values, but it was in range of 'ok').

I added the floater with brominating tablets, set about halfway open. Son and wife had a few soaks over the following two days.

  • I tested about 2 days after setting water initially, using the test kit and noticed bromine was ZERO or at least too low to measure.
  • Shocked with bleach as per above, bromine levels went back up to high as was normal for post-shock.
  • Overnight, bromine levels dropped to very low again. I believe son had a soak that evening also.
  • Shocked again, and adjusted the floater to wide-open / max.
  • Overnight, bromine levels dropped to very low again. Note: Water is crystal clear, nothing gross in filter at all, no abnormal smell.
  • Changed filter with a new one, and then super-shocked with 3 TBSP dichlor, left lid open all evening (not in direct sunlight), definitely smelled the chlorine, and once it was bedtime I tested with test strips and bromine was in range to close the lid, so I did.
  • Checked bromine just now (the super shock was last night)... back to negligible/zero.

What is going on here? Could the bromine tabs have become less effective as they were possibly frozen over the winter in the garage? Or should I use a spa purge/flush product and superchlorinate again to clear any possible issues from the plumbing?

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Replying to myself here...

I read the Decontamination post and will be doing an Ahh-some purge tomorrow evening (it's on order from Amazon now). 

There's gotta be something in these lines that's eating up the bromine.

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