Indoor Pool Loosing CYA and FC

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Isaac-1

Isaac-1

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May 10, 2010
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SW Louisiana
I came home to low CYA and FC a week ago after being out of town for a few days, the low FC was due to my chlorine metering breaking. (CYA of much less than 20, FC =.5 CC=3 ) water was cloudy. I shocked the pool and added stabilizer and thought I had it under control for a Pool Party on Sunday afternoon. After the pool party I brought it back up to shock level of 8.5+ and have tried to maintain it there for the last 5 days, however I have been loosing lots of FC per day (4.5 ppm on average), I have no CC showing on now, but my CYA is still showing less than 20 even though I added enough Stabilizer last weekend to boost it by about 15 ppm. Tonight I am adding 2 pounds of dichlor shock to boost the FC and CYA back to shock level, it had dropped to 5 ppm since this morning when it tested at 9 ppm.

any thoughts
Ike
 
It sounds like you either got a nascent algae bloom and/or bacteria started to convert CYA into ammonia. That would explain the high CC. You just need to keep adding chlorine until you get through the ammonia and partially oxidized CYA. If you want to know how much that will likely be, you can do a bucket test where 1/4 teaspoon of 6% bleach in 2 gallons of pool water is 10 ppm FC. Or just keep adding chlorine -- it will eventually hold. I'd wait on increasing the CYA until you clear the pool and get the chlorine holding -- a higher CYA will just slow things down or require you to have a higher FC that eventually you'll have to lower and being an indoor pool that would need a chlorine neutralizer so there's no need to set things up that way which will end up costing more.

Since you have an indoor pool, you might have a harder time getting rid of some of the CC depending on exactly what it consists of. With an indoor pool you often need to use a supplemental oxidizer of some sort. I see that you will be getting an ozonator at some point.
 
Thanks for the thoughts Chem Geek, it confirms what I have been thinking, the strange thing about this is I have had less than .5 ppm of CC showing since last Saturday. (I should also mention I used a couple of pounds of MPS shock last weekend before the pool party to help try to get things stable). I will keep it at shock level until the Chlorine demand drops off, I have a 2 pound container of Chlorine reducer (local pool store sells them for $7) that will drop my FC by about 5 ppm, which should help getting the FC down to swim safe levels once it is holding steady without having to wait a week or more to burn off a 3-5 ppm drop from shock level.

Ike
 
I wish you had mentioned the use of non-chlorine shock initially because as was just noted, MPS registers as CC in the chlorine test. You need to get the Taylor K-2042 MPS interference remover in order to properly distinguish between real CC and MPS, especially if you plan on using MPS in the future.

Now using MPS wouldn't have the FC drop as fast as you are seeing so you still need to deal with that the way we described. I'm guessing that the CC dropped so quickly because the MPS got used up oxidizing whatever is making the FC drop (i.e. using up chlorine). Whatever this is, it's not showing up as CC itself so it could be partially oxidized CYA fragments (Biuret, Allophanate-) as that would be consistent with what happened to me where I continued to have to add chlorine even after any ammonia or CC was registering (see this post).
 
Sorry for the delay getting back to the topic, some health issues came up I am having to deal with. Well it has been a month and my pool issues are continuing, (Chemgeek, I do have the K-2042 test kit), the water is clear and there have been no more signs of elevated CC since the swim party a month ago. However Chlorine (Bleach) usage is running much higher than it did this time last summer (nearly double), also it appears that I added a bit too much stabilizer getting ready for the pool party, 1 week after the party it tested just above 30 ppm ( tested 3 times over 4 days,, reading just under 30 at first to just over 30 at the end of the 4 days). Last weekend the CYA level tested out between 20-30, I would guess 25 ppm, and as of last night it is down to slightly under 20 ppm again. There has been minimal water replacement , CC has read less than .5 at all times, no MPS or other chemicals have been used since the swim party, just bleach, pH has been a steady 7.4

Ike

p.s. I will try to find an amonia test, and I should note I don't appear to have any algae problems at this point, no issue with DE filter clogging any faster than normal, no heavy bather load, if anything less than I had this time last summer.
 
Thanks for the reply, I will lower my targeted FC to the low side of the target per the CYA chart, but keep it above minimum, I had been targeting 4.0 FC based on the 30+ ppm CYA up until the CYA test from a couple of days ago..
Ike
 
Actually, I misread your post thinking the FC was high at 30 ppm. I don't think that 4 ppm FC with 30 ppm CYA is so bad and normally that should not be having the CYA drop noticeably. Even in spas with 2-4 ppm FC and 20-30 ppm CYA at hot temperatures they don't usually see CYA drop by more than 5 ppm per month.
 
I'd be interested in knowing why the use of CYA at all in an indoor pool.

I know that some states ban CYA in public indoor pools.

Since we don't have to protect the chlorine from sunlight, are we using the CYA in an indoor pool to provide a greater margin of error in chlorination?
 

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You can, of course, not use any CYA in an indoor pool or any pool not exposed to sunlight, but if you do so and don't keep the FC level extraordinarily low, then the active chlorine (hypochlorous acid) level will be much, much higher. The same regulations in some areas that prohibit or recommend against using CYA in indoor pools also have an FC minimum of at least 1 ppm. This results in the active chlorine level being over 10 times higher than in a pool with CYA that has enough FC to prevent algae growth (in outdoor pools). This higher active chlorine level oxidizes skin, hair and swimsuits faster as a result. It chemically reacts over 10 times faster to create disinfection by-products such as THMs from skin. It also outgasses chlorine faster.

The regulations on CYA only think of CYA as protecting chlorine from sunlight with little understanding of the chlorine/CYA relationship and how most of the chlorine is bound to CYA resulting in much lower active chlorine levels as a result. In Europe, especially in Germany, the commercial/public pool standard does not use CYA, but as a result they try to minimize the active chlorine level by having a lower FC range of 0.3 to 0.6 ppm if no ozone is used or 0.2 to 0.5 if ozone is used. Also note that the regulations of commercial/public pools in the U.S. do not account for the chlorine/CYA relationship even when CYA is used since they simply give ranges of FC with ranges of CYA rather than specifying an FC/CYA ratio range which would give much more consistent disinfection and oxidation rates.

It is true that a pool not exposed to sunlight will often need some form of supplemental oxidation, such as UV or ozone or non-chlorine shock (MPS), and that lowering the active chlorine level using CYA makes the oxidation rate from chlorine that much slower. So using supplemental oxidation for indoor pools makes a lot of sense. Ike, if you aren't using supplemental oxidation, then you should probably target something like 4 ppm FC with 20 ppm CYA to have a somewhat higher oxidation level and should seriously consider a supplemental system. Even those not using CYA often find problems with CC and smell in indoor pools

My wife has personally experienced the side effects of this rule where her swimsuits degrade (elasticity gets shot) and her skin is flakier and hair frizzier when using an indoor pool with 1-2 ppm FC and no CYA over the winter while in our own outdoor pool with an FC that is between 7.5% and 15% of the CYA level the swimsuits last for many seasons with no noticeable degradation and her skin and hair are not as affected by the chlorine in the pool.
 
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