After a broken heat exchanger, my (in-ground, 700 gal, fiberglass) tub sat covered with partial water for 2 months. Big mess to clean up now. So after draining and cleaning any staining with diluted (1 Tb acid:2 c water) muratic acid (and rinsing), the tub was looking good. Filled with water and went through the following steps, but I cannot get a bromine level to build/show and there is also a light gray cast/staining over most of the area:
08/17/14 1500: Test: pH=7.7, Alk=40, CH=30, TDS=55 (fill water)
08/18/14 1500: Test: pH=7.8, Alk=50, TDS=111 (circulated fill water, 24 hr)
I assume 56 ppm of "stuff" came from the lines/filter?
08/18/14 1645: Add 10 oz driveway de-icer (thought was CaCl) for CH target of 130
08/18/14 1845: Test: pH=7.8, Alk=50, CH=50 (!), TDS=217
Apparently 106 ppm "stuff" added (as expected), but only ~20 ppm Ca - Turns out the primary ingredient was Sodium Chloride. Also has MgCl.
08/18/14 1915: Add 8.2 oz sodium bicarbonate for TA target of 100
08/18/14 2030: Test: pH=8.0+, Alk=100, TDS=273
08/19/14 1015: Add 3.5 oz sodium bromide to establish the bromine bank; circulate on high
08/19/14 1115: Test: pH=8.0+, Alk=100, TDS=305, AD (Acid Demand) =1-7.8 or 2-7.4
This was supposed to make a 30 ppm bank, but the measurement indicates around 30 ppm of combined sodium and bromide ions, right? So less Br(-)?
08/19/14 1115: Add 16 oz Spa Choice Metal Free
08/19/14 1145: Test: TDS=308
Apparently there was no copper etc. present since there was no reduction in the TDS. Reasonable?
08/19/14 1400: Add 3.0 oz MPS to shock
08/19/14 1530: Test: pH=7.9, Alk=100, Br=0, AD=1-7.6
Light gray staining everywhere
08/19/14 1700: Add 3.6 oz MPS
08/19/14 1800: Test: Br=0
So the issues: 1) why can't I get the bromine level up? Is the Br being used up by contaminants left over from the lines/filter? Should I just keep keep repeatedly shocking until everything dies off and the Bromine level stays up?
As far as that, I'm afraid of dropping the pH too much with multiple applications of MPS. I had the thought of alternating MPS with bleach to move the pH as needed. Thoughts? I'm trying to stay within +- 0.5 saturation index from the Taylor sliding wheel chart (temp of 80 *F), but don't really like the idea of putting more of the driveway melt in -- I think the MgCl is making it harder to do an accurate hardness test.
If I put more than enough bleach to oxidize the bromide bank into a sanitizer, will the "excess" bleach that hasn't been used to oxidize the bromide also sanitize? Also, I presume that excess bleach (not used as a sanitizer itself) will immediately re-oxidize any bromide arising from the bromine sanitizer being "used", correct? Or is it best to keep the bleach under the bromide bank level? Should I increase that bromide bank level?
Second issue: 2) why would shocking cause staining? I'm less bothered by it, but just as confused. The TDS readings should pick up metals like copper, shouldn't they?
Would really appreciate your thoughts!