Pink "Algae" and Sodium Bromide

[TreeFiter]

I just picked up a customer that is fighting pink "algae" in his pool. Hundreds of dollars have already been wasted trying to treat this pool using conventional pool store wisdom. He had been shocking the pool almost daily with dichlor and trichlor, so the CYA was up to 100. He has been burning through chlorine tablets extremely fast. He said he had to refill his chlorinator daily, and he had two floaters in the pool, yet he still couldn't get the chlorine to stay in the pool.


So I added liquid chlorine to bring the FC up to about 60, and I'm going to keep it up there until it passes an OCLT.

Today I read something about pink "algae" and it talked about Sodium Bromide, and said that using Sodium Bromide would eat up a lot of chlorine. Is this true? Could it be that the Sodium Bromide is causing the difficulty with maintaining FC in this pool?

In any case, I think my best course of action is to continue to SLAM and brush the pool.

 

[JVTrain]

Sodium bromide will yield bromide ions in pool water. Bleach will oxidize bromide ions to hydrobromous acid. This is the mechanism used to maintain some hot tubs/spas. The hydrobromous acid will register just like FC on a FAS-DPD chlorine test or OTO test (just that the scale for Free Bromine is 2x the Free Chlorine scale). So yes, sodium bromide will "eat" bleach but only as to convert bromide to another form that still registers and sanitizes in a similar way to free chlorine, without the protection of CYA that FC gets. Sodium bromide would only be present if it were intentionally put in the pool such as with bromine tabs or actual sodium bromide.

I know nothing of this pink algae... is that in a My Little Pony episode?

 

[TreeFiter]

When the reaction occurs and the Sodium Bromide uses up some chlorine, wouldn't the test still show FC (even though its really Hydrobromous acid). In other words, a test strip would still show something is there, and so would a FAS-DPD test.

I guess your point about the lack of protection from CYA could explain it though. If the chlorine is used up oxidizing the bromide ions to hydrobromous acid, and then the sun destroys the hydrobromous acid within an hour or two, there would be a low or even zero reading for FC.

So the next question is, how much FC would I expect a given amount of Sodium bromide to consume? It sounds like this pool (20k gallons) has had several treatments with Sodium Bromide, each container appears to be about 2 lbs. Also, if I understand correctly, in hot tubs, the bromine pretty much remains in the water and needs to be "activiated" with an oxidizer, usually chlorine or MPS. This activation process sounds similar to the oxidizing of bromide into hydrobromous acid. Does this mean that this pool will be stuck in this loop of using up an amount of FC to oxidize bromide, only to have the sun undo the process almost immediately after? In other words, it sounds like I'll have to add more chlorine regularly to get the same net result in terms of FC.

Will the bromine eventually get used up or find its way out of the pool, or will I have to drain and refill to get rid of it?

 

[JVTrain]

Right. The bromide would consume the chlorine you added until all bromide was converted. Then if you added more bleach, you'd have free chlorine as well as hydrbromous acid.

Bromine is not typically used in outdoor pools because there is no CYA equivalent for bromine.

Once a bromine spa (pool) always a bromine spa (pool). The only way to remove bromide is to drain. Chem geek is more educated in the bromide dynamic than I am but that's the gist of it.

 

[TreeFiter]

Now this is getting interesting (its also bad news, but still very interesting). So there is no way to know if I'm dealing with bromine or chlorine, or how much of each, assuming both are present. So if I add chlorine to oxidize the bromine, and I end up with a test result of lets say 10ppm, I have no way of knowing if I have high bromine, or appropriate chlorine levels based on high CYA levels.

I read in another post that bromine will out gas slowly over time, especially if aerated. This pool a is significantly aerated, so there might be hope. If not, I believe they are considering refinishing the pool bottom soon, so they might only have to suffer through the rest of this year with it.

 

[mickey4paws]

If I remember correctly pink algae isn't really algae, but rather is a bacteria. Have you ever seen a pinkish ring around your bathtub drain and if you scrub it, it goes away? I believe that's the same "pink algae" referred to in pools. When we used to keep our solar cover on too much, we would sometimes get a little pink on the ladder and also on the string holding the thermometer. But we haven't had any of this pink stuff this year and I imagine it's because we don't use the solar cover much.

 

[chem geek]

There are two products that are used to fight algae in high CYA pools: sodium bromide and ammonium chloride. They both work the same way in that when these are added to a chlorine pool (or chlorine is added to a pool with these products) they produce chemicals that do not bind to CYA so are not cut down in their strength, namely bromine and monochloramine. The problem with sodium bromide is that it won't go away so when bromine gets used up it becomes bromide. That is what is meant by once a bromine pool always a bromine pool. Yes, bromine will slowly outgas over time but that could take weeks or months depending on how much bromide you added. At least with ammonium chloride the monochloramine can get oxidized by adding additional chlorine. Monochloramine is more effective against algae than against bacteria. And yes, with bromine you can't distinguish it from chlorine.

Since pink slime is caused by a bacteria, it is usually handled fairly readily by chlorine, so your shocking with a high FC should get rid of it. However, not being able to keep chlorine in the pool is more likely to be from nascent algae growth so your SLAM should help with that as well. It's also possible that sodium bromide was already added to the pool in which case you'll have greater chlorine loss since bromine breaks down in sunlight faster than chlorine (at least chlorine when CYA is present).

 

[TreeFiter]

The initial OCLT actually showed a slight increase in FC from 56ppm at sunset, to 59 the next morning. Such a small change could simply be due to small errors in testing, but I'm somewhat reluctant to trust that OCLT because I added enough chlorine to raise FC way above 56, probably closer to 90. Some FC was most likely consumed by the bacteria or any algae in the pool. However, this pool has limited circulation with only a skimmer and a return, so it is possible that the initial test for FC didn't account for all of the FC in the pool because it didn't mix thoroughly. I did a follow up at the end of the day, just before sunset, and the FC had dropped from 59 in the AM to 48. It was a cloudy/rainy day with limited sunlight, but I was expecting a much bigger drop, even with the CYA at 100. I'm going there shortly to see if there was any change last night. This should be a more accurate OCLT than the first.

In practical terms, how difficult will it be to manage chlorine/bromine levels in this pool once the algae/bacteria issues are solved? I won't be maintaining this pool long term, but I want to be able to leave the owner with a plan that he can handle himself. Is this the kind of thing where he will need to refill his chlorinator daily, or should he still be able to fill it once a week and forget about it.

 

[chem geek]

Once bacteria and algae are killed then the pool should be like any other. The main issue is the high CYA so a proportionally higher FC would be needed unless supplemental products are used to prevent algae growth (i.e. Polyquat 60, phosphate remover, etc.). If the owner is willing to add chlorine every day or two, then they can just follow normal TFP methods. Of course, if he refills his chlorinator with Trichlor tabs, then CYA will likely continue to climb unless he's got extraordinary water dilution.

 

[TreeFiter]

So the fact that there is Bromine present isn't going to make a big difference? I plan on coaching him a bit on how to manage his chlorine levels, but I have a feeling he will continue to use tablets. He may be willing to replace some water, but I'm pretty sure he has iron in his well, which would bring on a new set of problems. For now, one thing at a time. The pool went from 38ppm FC this morning down to 8ppm tonight. I'm going to have to bring it back up in the morning.

 

[chem geek]

I don't know how much sodium bromide product you added. If he's got bromine in his pool he may notice a higher loss so greater amounts of chlorine to be added, but hopefully over the next weeks that will return back to normal (unless a lot of bromide was added in which it could take months).

 

[TreeFiter]

At least 4lb of 88% Sodium Bromide was added to a 20,000 gallon pool. I didn't add it. The customer called me because he had thrown just about everything he could find in this pool, and nothing had worked for him. The one thing that might save this pool is that instead of normal returns, this pool has a homemade fountain on the return. There is a T with 4 foot long pipes with holes drilled along each side so the water comes out in numerous streams like a fountain. So there is significant aeration happening.

Another interesting thing about this situation is that I was referred to this customer by another pool guy I work with. When he told me about this pool, he was freaked out because of the phosphates in the pool. He presented me a theory about how when the pool was refinished a few years ago, it was done by a guy with a reputation for doing bad work. He suspects that one of the chemical treatments he used contained phosphates, and caused all these problems. There have also been some issues with chalky residues on the surface, and clouding when the walls are brushed. I think its all related to the pink slime. The customer even did an experiment where he compared phosphate levels in a sample of water from the pool, and tap water in which he rubbed the walls and then rinsed his hand with the tap water sample. The tap water sample tested extremely high for phosphates where the pool water was fairly low. I suspect since algae eat phosphates, there would be a high concentration on the walls where a biofilm was forming. Have you ever heard of phosphates leaching out from a paint job in a concrete pool? It seems unlikely to me. I realize the phosphates should be irrelevant, but this idea has already been planted in the customer's head that the paint job could be causing him problems.

 

[chem geek]

Wow, that's 21 mg/L sodium bromide so 16 mg/L bromide. Normally, one only adds enough for a few ppm bromide since only a few ppm bromine is needed. Well, this could take many months if not years as a bromine pool if there is not significant water dilution. Aeration will only help a little since bromine doesn't outgas that quickly -- it will help, just not hugely. On the plus side, the active bromine level is not affected by CYA so will be strong and likely prevent algae (and probably pink slime). On the downside, the amount of chlorine (or other oxidizer) dosing needed to maintain a disinfectant level will probably be higher than before due to faster breakdown from the UV in sunlight.

As for the phosphates, they do not cause algae. They just provide algae food. The real cause of algae was improper maintenance of the FC/CYA ratio. Basically, for people who refuse to properly manage their pools that's when the extra-cost algaecides or phosphate removers can be useful in specific situations. So for a pool service, it's an option. However, for this pool where tap water is high in phosphates then a phosphate remover isn't as good an option since with evaporation and refill phosphates will constantly be being re-introduced (if one regularly adds a phosphate remover, then the water may be more frequently cloudy from it or it can clog up the filter more frequently). And yes, algae will consume phosphates and nitrates as part of their growth. I haven't heard of phosphates leeching from a pool surface, but it can be released (some) from algae when shocking to kill them.

The bottom line is that this customer did not maintain the proper FC/CYA ratio. The phosphates did not cause the problem though they are a necessary requirement for algae to be able to grow IF the active chlorine level is kept too low.

 

[TreeFiter]

Wow, that's 21 mg/L sodium bromide so 16 mg/L bromide. Normally, one only adds enough for a few ppm bromide since only a few ppm bromine is needed. Well, this could take many months if not years as a bromine pool if there is not significant water dilution. Aeration will only help a little since bromine doesn't outgas that quickly -- it will help, just not hugely. On the plus side, the active bromine level is not affected by CYA so will be strong and likely prevent algae (and probably pink slime). On the downside, the amount of chlorine (or other oxidizer) dosing needed to maintain a disinfectant level will probably be higher than before due to faster breakdown from the UV in sunlight.

As for the phosphates, they do not cause algae. They just provide algae food. The real cause of algae was improper maintenance of the FC/CYA ratio. Basically, for people who refuse to properly manage their pools that's when the extra-cost algaecides or phosphate removers can be useful in specific situations. So for a pool service, it's an option. However, for this pool where tap water is high in phosphates then a phosphate remover isn't as good an option since with evaporation and refill phosphates will constantly be being re-introduced (if one regularly adds a phosphate remover, then the water may be more frequently cloudy from it or it can clog up the filter more frequently). And yes, algae will consume phosphates and nitrates as part of their growth. I haven't heard of phosphates leeching from a pool surface, but it can be released (some) from algae when shocking to kill them.

The bottom line is that this customer did not maintain the proper FC/CYA ratio. The phosphates did not cause the problem though they are a necessary requirement for algae to be able to grow IF the active chlorine level is kept too low.

I don't think the tap water has a phosphate problem. What I was describing was an experiment the owner had tried in which he took a sample of tap water, assuming it was essentially clean water, and he rubbed his hand on the pool wall, which left a chalky residue. He then rinsed the chalky residue with the tap water and then tested it for phosphates. This is how they concluded that the paint was the source of the phosphates. I'm not convinced of it yet, but there is definitely a bit of a chalky residue coming off the walls. I would think that shouldn't be the case in a relatively new paint job.

I'm not worried about the phosphates. I'm aware that they don't cause the problem, and I avoid using phosphate removers unless there is a good reason. Like you said, they can be useful in specific situations, but usually shouldn't be necessary.

You are right about the FC/CYA ratio being the cause of the problems. Unfortunately he went to the company I work for, and they gave him bad advice. I'm having trouble getting anyone to listen to me when I tell them why things keep going wrong. He threw a whole bunch of trichlor shock at it, a few pounds at a time, and when that didn't work they sold him sodium bromide. Its no wonder customers are contacting me to straighten out their pools on the side rather than hire my employer. So now his CYA is 100 ppm, whereas if he had good advice when the problem first started, he could have solved the problem fairly easily and avoided the high CYA and now bromine issues.

I plan on explaining to him just how much easier things would have been if he came to me sooner. Maybe I can save him from the next big problem before the pool store messes it up for him. He does have some iron issues that I might be able to help him with. He's already done AA treatments to remove stains, but I see staining starting to come back already.