Cannot raise Bromine level & staining

[dakinemaui]

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!

 

[chem geek]

Welcome to TFP!

I assume 56 ppm of "stuff" came from the lines/filter?

Tap water typically has some calcium and bicarbonate and some salt (mostly sodium chloride) all of which will contribute to TDS.

Apparently 106 ppm "stuff" added (as expected), but only ~20 ppm Ca - Turns out the primary ingredient was Sodium Chloride. Also has MgCl.

You should have used Peladow or Dowflake which are calcium chloride. All road salt is not the same, as you found out.

08/19/14 1015: Add 3.5 oz sodium bromide to establish the bromine bank; circulate on high
:
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(-)?

3.5 ounces weight of sodium bromide in 700 gallons is 99.22 grams in 2650 liters or 37.44 mg/L which is 37.44*79.904/102.894 = 29 ppm bromide. I believe when they talk about the bromide bank they refer to 30 ppm bromide. That would be able to make 15 ppm bromine (it takes two bromide to make a bromine molecule from which hypobromous acid, HOBr, is made and bromine measurements are in the weight of a bromine molecule).

Apparently there was no copper etc. present since there was no reduction in the TDS. Reasonable?

No, it doesn't work that way. There would only be a small amount of copper of perhaps 0.5 ppm or so to remove so would not be a noticeable change in the TDS and that would be for physical removal, not sequestering.

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?

Assuming the MPS you are using is 43% MPS, then 3 ounces should be equivalent in 700 gallons to 6.43 ppm FC or around 14.5 ppm bromine. What kind of test kit are you using? If DPD, then maybe the indicator dye is getting bleached out (though usually that needs a higher level for that to occur). Do you have a Taylor K-2006 or K-2106 or TFTestkits TF-100?

You can take a bucket of spa water and experiment with that to see if you can get a reading. If it takes a lot of oxidizer to get a reading, then you've got something in the water consuming a lot of oxidizer. Having sat with partial water for 2 months you may have significant biofilms. I suggest getting some Ahh-Some to get rid of greases, oils, and biofilm. Otherwise, you'll just be fighting that.

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.

Yes, you can alternate with MPS and bleach if you like, but the MPS will lower the TA which should reduce the amount of pH rise. If your TA gets to around 50 ppm, you could use 50 ppm Borates to help stabilize the pH and at that point may be able to just use bleach to create more bromine from the bromide bank.

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?

You usually have excess sodium bromide in the bromide bank so the bleach will make only bromine, but if your bromide bank got low then yes the bleach will disinfect as well -- you'll have chlorine as well as bromine at that point. So you usually just try and keep your bromide bank at around 30 ppm, but unfortunately there's no easy way to measure it. Spent bromine becomes bromide so the main ways the bromide bank gets used up is from bromine combining with some organics and getting filtered and removed, from bromine outgassing, and from some bromine getting converted to bromate though that mostly happens from reacting with ozone (do you have an ozonator?).

You can always add some more sodium bromide, say halfway between when you would do a water change. Excess sodium bromide is not a problem.

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?

I'm not sure what is causing the staining, especially since it's gray. It might be copper since that can be black instead of green in staining or it could be iron which similarly can sometimes be black instead of yellow/red in stain.

 

[dakinemaui]

Thanks SO much for the thoughts!!

Tap water typically has some calcium and bicarbonate and some salt (mostly sodium chloride) all of which will contribute to TDS.

The fill water TDS was 55 ppm. After running the pump for 24 hr, the reading was to 111. I attribute the increase of 56 ppm to whatever was in the filter/lines. That means more than 5 oz of "something" (probably something bad), right?

Assuming the MPS you are using is 43% MPS, then 3 ounces should be equivalent in 700 gallons to 6.43 ppm FC or around 14.5 ppm bromine. What kind of test kit are you using? If DPD, then maybe the indicator dye is getting bleached out (though usually that needs a higher level for that to occur). Do you have a Taylor K-2006 or K-2106 or TFTestkits TF-100?

Taylor K-2106 and test strips just for a sanity check

Technically it says 100% "MPS Compund" but later gives 43% Potassium Peroxymonosulfate. So I think that's what you mean. Those instructions say to add 1.5-2 oz per 500 gal weekly. Extrapolating from your figures, they recommend 6.43 * 2/3 * 700/500 = 6 ppm (FC) which seems quite low for a shock. Isn't 10 ppm FC the typical goal to oxidize waste?

You can take a bucket of spa water and experiment with that to see if you can get a reading. If it takes a lot of oxidizer to get a reading, then you've got something in the water consuming a lot of oxidizer. Having sat with partial water for 2 months you may have significant biofilms. I suggest getting some Ahh-Some to get rid of greases, oils, and biofilm. Otherwise, you'll just be fighting that.

Strong bromine reading with as little MPS as I could shake into 10 oz of water. (Probably less than you'd salt your food.) I have some enzyme product, so I'll try that. No ozonator, BTW.

Some other posts have recommended 50 ppm FC in similar cases. If I put that much 6% bleach (1/2 gal), would that not drastically raise the pH? (Currently pH=7.9, TA=100, no CYN).

 

[chem geek]

The TDS did not change by that much just from running the pump. That's a test kit error. How are you measuring the TDS?

As for how much oxidizer you add after a soak to handle bather waste, it depends on whether you have an ozonator. With no ozonator, the rough rule-of-thumb is that every person-hour of soaking in a hot (104ºF) tub requires around 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS). With an ozonator, only half the amount may be needed (in your case you said you don't have an ozonator). The real rule is to add whatever is needed to still have a small residual 24 hours later (say 2-4 ppm bromine).

Superchlorinating is not as effective as using Ahh-Some. And yes, it raises the pH but that also somewhat moderates the chlorine strength that is added. One can somewhat lower the pH before superchlorinating, but it's still going to go fairly high.

Note that if your pH tends to be high, you might consider lowering your TA level.

 

[dakinemaui]

The TDS did not change by that much just from running the pump. That's a test kit error. How are you measuring the TDS?

$30 digital pen meter on water sampled at about 18" depth. While it's not lab quality by any stretch of the imagination, it's been quite repeatable in the tests I've done with it. The kicker is that when I put X oz of a salt like Sodium Bromide, the increase is fairly in line with expectations. Given how these cheap meters work, I expect the actual "stuff" could be higher if there were non-charged particles involved, so I'm looking at that reading as a lower bound.

Looking forward to tomorrow. The Ahh-some should be here, and I can start making concrete steps toward improvement. Thanks again for your thoughts.

 

[chem geek]

Well maybe there was something in the lines after all if the measurement is that consistent and sensitive. Anyway, the Ahh-Some will get a LOT of junk dislodged from your piping given how long there was standing water in the spa.

 

[dakinemaui]

Any thoughts as to the Ahh-Some with a sand filter?

1) I currently plan to run it through the filter as normal while foaming, then shut the pump off and clean the goop.
2) Then set the plumbing to go straight from tub to waste (bypassing the filter).
3) Open the filter and clean as much goop as I can.
4) Put some clean water in the tub, and backwash (reverse through the filter) to waste.

Am I overthinking this? Will the goop collect in the top of the sand filter cavity?

 

[JVTrain]

I would not run the Ahh-some product through a sand filter. Run your filter on recirculate to bypass the filter during the treatment. Cartridge type filters you can remove from their installation location and drop them in the water during treatment but the enclosed sand filter... that will have undesirable results.

If you want to clean the sand filter, I would do it as a separate process. See the details on how to do this in a great thread by Smykowski. Deep Cleaning a Sand Filter

I have only used the Ahh-some product once, and will again soon so maybe chem geek can sign off on running it through a sand filter, but I wouldn't.

Also... yes, you're over thinking it, but that's better than under thinking!

 

[dakinemaui]

Thanks, JVTrain -- you guys are awesome. That sand filter thread is just what I need.

 

[chem geek]

I'm confused. You have a sand filter with your 700 gallon hot tub? There is an Ahh-Some product for filters and this works for sand filters as well. You will notice that the instructions for the general water and pipe purge Ahh-Some product has a clarifier in the gel that is intended to capture what gets dislodged so it gets trapped in the cartridge filter.

I would just follow the procedure in the Deep Cleaning link for the sand filter. As for using Ahh-Some for the spa proper, you should not need to bypass the filter since the clarifier is designed to catch the gunk into the filter so you should backwash and then do the Deep Cleaning procedure AFTER using Ahh-Some for the general water, spa surfaces, and piping. You'd normally only use the Ahh-Some filter product if you had some nasty clumping sand with biofilms and didn't want to replace the sand.

 

[dakinemaui]

Yes, sand filter (Pentair TR-100C) for the 700 gal tub. (Don't get me started about that contractor...)

Followup: I ran the Ahh-some with the pump set to Recirculate and got a disappointing amount deposited at the waterline (nothing like the video, but it was green and yucky). I then backwashed/drained this Ahh-some-laden water through the filter. Not much bio-gunk to speak of in the filter. HOWEVER, the sand was bright blue (from several previous heat exchanger meltdowns -- a topic for another discussion) and extremely hard. So I bit the bullet and replaced all the sand, acid washed the staining out of the tub, and refilled.

At that point, I did NOT decontaminate. I thought that replacing the sand and flushing the plumbing would be enough, but I was still having a hard time getting the bromine level up to acceptable levels. I would add enough bleach for 10 ppm Bromine and measure 2 ppm when tested an hour later. Similar on two additional attempts. Decided to decontaminate after all, but I only had enough bleach left for 41 ppm FC. After an hour, FC was 11.6 (actually measured Br at 26, but I might have made an error so I don't actually fully trust this number -- it might be off by 2 ppm Br because I can't count). Since it didn't seem "bad" for the tub at that level, I didn't bother to drain and just let it "cook". Another hour later, the FC was 9.8 (which I do trust).

(FWIW, I was expecting high levels, so I diluted the spa water to read 5 ppm bromine per drop with Taylor 2106: mixed 25 g spa water + 75 g chlorine-free water, and then used the 10 ml Taylor test line (1.25*4=5 ppm/drop). Once I realized the reading was not nearly as high as expected, I switched to the 25 ml line (0.5 * 4 = 2 ppm/drop).)

Ideally, I would drain this water, but I'm trying to be somewhat sensitive to cost and waste. My plan is to see how much is left 24 hr after the 9.8 FC reading. If it's above 5 ppm, I think I'll just balance and call it good under the assumption that any debris is effectively "gone". Perhaps weekly shock at 15 ppm FC a few times to "make sure".

If the FC is under 5 ppm after 24 hr, then I guess I'll drain it. I would guess that there's nothing alive at this point, but the continued chlorine demand is due to oxidization of the remaining waste. Presumably, draining will get rid of that waste faster than trying to oxidize it.

 

[chem geek]

Yes, that sounds like a decent plan.

 

[dakinemaui]

Good news -- FC was 6.1 this morning (9.8 yesterday am), so chlorine demand of 37%. So glad I don't have to drain again!