Struggling to maintain chlorine after algicide

[GeoffM]

I forgot to check the chlorine tabs in my pool before we went away for a few days. When we came back the pool had large patches of yellow algae. I've had it before but a quick shock, algicide, and scrub and it's gone. The tabs keep the chlorine level at around 2.5 using the dropper test kits, but when we came back it was virtually zero. Added tabs, shock, and got it back up to 2.2-2.3. Went to the pool store to buy algicide with a water sample and they agreed with the results. PH 7.3, everything within range, though I forgot to ask about CYA testing.

Dumped 1.5 capfuls of granular algicide in per instructions (15,000gal - I think, very irregular shaped pool) followed by 3/4gal of liquid chlorine, again per instructions. Tested chlorine an hour later and it was at 2.0 so dumped the remainder of the liquid chlorine in. Tested again an hour later and still about 2.0 so this time dumped a pound of granular chlorine in (ran out of liquid). An hour later again and still 2.0!

I thought I needed to shock the pool but I haven't even gotten it out of the "safe for swimming" range! I can dump more chlorine in but something is not right when I've already added way more chlorine than instructed to little avail.

Do I need to go and buy more liquid chlorine, or am I missing something?

As an aside the pool is slowly clearing so the algicide and filter seem to be doing the job.

Thanks. Lots of questions and answers about algae but couldn't find anything about maintaining the chlorine level after.

 

[kabutotx]

Which algaecide?

 

[GeoffM]

Which algaecide?

United Chemical Yellow Treat
(Sodium Bromide)

 

[Donldson]

Oh no...

As soon as I read the title I knew you added sodium bromide "algaecide". The sodium bromide you added is still in your pool, and there is only one way to remove it. As you add chlorine it reacts with the bromide to create bromine. Bromine is not stabilized against UV degredation the way CYA does with chlorine, so the bromine quickly burns off in the sunlight. As the bromine burns off it reverts to bromide, which is then reactivated almost instantly by chlorine to make bromine again. This continues until most all of your sanitizer burns off. This will continue consistently every day until the bromide is removed from the water.

Fastest fix? Dump your entire pool and start over, and NEVER use Yellow Treat again.

 

[kabutotx]

OK. You now have bromides in the pool. It didn't sound like you added much but I'm not an expert on bromine pools.
Basically, chlorine turns your bromides into bromine. With a FAS-DPD test you are supposed to be able to read bromines just like regular chlorine.

 

[GeoffM]

Oh no...

As soon as I read the title I knew you added sodium bromide "algaecide". The sodium bromide you added is still in your pool, and there is only one way to remove it. As you add chlorine it reacts with the bromide to create bromine. Bromine is not stabilized against UV degredation the way CYA does with chlorine, so the bromine quickly burns off in the sunlight. As the bromine burns off it reverts to bromide, which is then reactivated almost instantly by chlorine to make bromine again. This continues until most all of your sanitizer burns off. This will continue consistently every day until the bromide is removed from the water.

Fastest fix? Dump your entire pool and start over, and NEVER use Yellow Treat again.

Eek. Silly question: why did the pool store sell and recommend it (not even their most expensive product) if this happens? Or did I do something (else) wrong?

Water is expensive here so is that really the only solution?

 

[Donldson]

Great question. In a pool that is overstabilized it does help clear it, but completely hoses the chemistry in the process. Kind of like a payday loan, you fix the immediate problem but end up creating a new ongoing problem. It isn't even an algaecide, if you add sodium bromide to a pool with no chlorine it will do precisely bupkis to the algae. I don't know why companies sell it as such, it really is one of the worse things we are seeing being sold nowadays.

There is no way to solve the problem without lowering the bromide level and there is no way to lower the bromide level without draining the water. Even a tiny bit of bromide can cause the problem, so while you could try a partial drain and see if that helps, if it doesn't you will need to do another partial drain. I do really wish I had some better news, but you are the second person in the past 24 hours to have this problem and he already has done several partial drains and still is having trouble.

In the future, I would just avoid all algaecides and stick to SLAM Process for algae problems.

 

[GeoffM]

Live and learn. Armed with the bromine thing I did some more searching on this site and now know a lot more than before, unfortunately way too late. (And before anybody asks, no it wasn't that nationwide chain of pool suppliers but a local one-location-only store). I'll try a partial drain first and test chlorine a few times a day. The pool does get full sunlight nearly all day long which other threads here seem to suggest might help.

If I can maintain a safe chlorine level without throwing excessive money/chlorine at it, is that sufficient for the next two weeks? Water rates are tiered so it's cheaper to do it on the 30th-1st of the month to spread it over 2 "months".

Thanks everybody.

 

[lightmaster]

If water is expensive where you live, it's probably better to just drain it all and refill and be done with it. If you partial drain and refill, and it doesn't work, you'd be using 50% more water. I don't know much about gunite, and idk the temps where you live, so be careful about it drying out and cracking. Might try draining in late afternoon and through the night, using a hose to keep walls damp while draining. Try to refill it quick as you can once all the water is done, and you can get a splitter and hook up 2 hoses to fill faster.

 

[Donldson]

The pool does get full sunlight nearly all day long which other threads here seem to suggest might help.

Not quite sure what you mean by that, full sunlight is the worst situation to have bromide in a pool. Bromine burns off in sunlight same as chlorine, but CYA helps stabilize chlorine and protect it from the sun but it does not do the same for bromine. As far as who owned the pool store, well I can't speak for everyone but I refer to all pool stores the same way. I dislike them all equally unless an individual one gives me a reason to dislike them even less. It is a shame the owners of your pool store don't care enough to learn the downfalls of the stuff they are selling, especially in a part of the country where water is not cheap.

You can try to keep the chlorine level adequate per the [FC/CYA][/FC/CYA] and try to wait out the end of the month, but you are going to continue to see that rapid chlorine loss. I do hope you are able to, I understand water can be expensive in parts of the country. Best of luck!

 

[GeoffM]

24 hours since my OP and the situation is this: no chlorine or anything else added (just a couple of regular 3" tabs floating) and chlorine level was about 2.0 this morning, only a tad below last night. I thought I might have gotten lucky but knew that sunlight would burn off chlorine. Indeed just now, 5pm local, the level was closer to 1.0, so maybe not so lucky after all.

Sparkling blue pool again though. <wry smile>

 

[GeoffM]

Question: if I'm using the "yellow test tube" dropper test and it comes up around 2.0, am I measuring chlorine or bromine (at a higher value)?

FWIW it seems to be holding around this level for the last 72 hours with just the 3" chlorine tablets.

Another question: why is sodium thiosulphate not a recommendation if it neutralizes bromine (and chlorine)? I'm aware it has to be used in a test-dose-wait-test-smallerdose-wait-test-smalleragain cycle. Just curious.

 

[Donldson]

Question: if I'm using the "yellow test tube" dropper test and it comes up around 2.0, am I measuring chlorine or bromine (at a higher value)?

You are measuring bromine and chlorine with either the OTO or FAS-DPD test. Essentially bromine is first, since the chlorine will react with bromide and create bromine. How much? Depends on how much bromide is in the water. Then the rest remains as chlorine. As bromine is used up it reverts back to bromide and if there is chlorine in the water that will react with the bromide to create more bromine. Lather, rinse, repeat. There is no way to tell how much of each is in there by the tests.

No idea about sodium thiosulfate, it is almost never needed since chlorine levels will drop on their own and there are rarely cases where the FC level is so high as to warrant that kind of concern. For those rare times when chlorine levels do need to be dropped quickly we tend to go with hydrogen peroxide.