Is All Cya Created Equal?

[mlobitz]

I have a SWG pool, but it's winter so the cell is powered down. I have been using a trichlor 1" tablet floater to keep the algae at bay for the past week or so. Can I use the CYA stabilizer that is going into the water as my stabilizer for the season when I'm done with the floater assuming that when I power up the SWG the CYA reading are at say...50 ppm to 80 ppm. The pool receives direct sunlight all year round weather permitting.

Also...I have a 500 gallon spa that is covered by an insulation cover and is under a patio cover meaning it never has direct sunlight hitting the water at anytime. Do I need as high a level of CYA in that water. Dichlor, of course, cranks up the CYA, can I just go to bleach at refill or is that too strong? Do I need to get to 30 ppm if there is no sunlight hitting the water at any time?

Thanks!

[Richard320]

Oooh! Ooh! I know the answer to this one!

Yes, it is all the same CYA.

My pool suffers from a surplus of CYA thanks to the previous owners' apparently exclusive use of a tablet floater.

So yes, if you get the CYA level up to some point using the fgloater, you don't need to buy special stabilizer powder

[chem geek]

FYI: For every 10 ppm Free Chlorine (FC) added by Trichlor, it will also increase Cyanuric Acid (CYA) by 6 ppm. The CYA will not go away (much) except from dilution of the water.

[mlobitz]

No offense to either one of you...thank you for your replies, but neither of you answered my question about the spa...any thoughts about that?

Also, do I need to add stabilizer(CYA) to the pool if the floater gets me up to 30 ppm - 80 ppm? I understand all the conversions, so that's not the issue, it's just a simple yes or no...add it, don't add it...take it back to the pool store...just need a little advice on those things...

Thanks!

[mlobitz]

Oooh! Ooh! I know the answer to this one!

Yes, it is all the same CYA.

My pool suffers from a surplus of CYA thanks to the previous owners' apparently exclusive use of a tablet floater.

So yes, if you get the CYA level up to some point using the fgloater, you don't need to buy special stabilizer powder

Sorry I missed your last line there. Thanks for answering my question. So if I get my CYA up with the floater each year, then I don't need the stabilizer. That's pretty cool. Kill two birds with one floater. Algae in the winter and plenty of CYA for the SWG in the spring, summer and fall. Cool...

[chem geek]

No offense to either one of you...thank you for your replies, but neither of you answered my question about the spa...any thoughts about that?

You do not use bleach after the refill (except for decontamination which is relatively brief) since it will be too strong. You should use Dichlor first to get the CYA up to 30 ppm (so cumulatively add around 33 ppm FC worth of Dichlor, usually about a week or so) before switching to bleach. This is all explained in Nitro's Approach to Water Maintenance.

[mlobitz]

No offense to either one of you...thank you for your replies, but neither of you answered my question about the spa...any thoughts about that?

You do not use bleach after the refill (except for decontamination which is relatively brief) since it will be too strong. You should use Dichlor first to get the CYA up to 30 ppm (so cumulatively add around 33 ppm FC worth of Dichlor, usually about a week or so) before switching to bleach. This is all explained in Nitro's Approach to Water Maintenance.

Thanks! I've read through the N.A.t.W.M. which is great, but I'm just curious about the UV issue. If the CYA is a stabilizer in the pool for chlorine coming out of the SWG, is it there to protect users from high levels of chlorine or is it to protect the chlorine from UV light? Or...is it both? My spa is covered from the sun, so no UV, or very little UV hits the water. I understand that straight bleach is too strong, but I was curious about the reasons behind it. Sounds like a little of both. Protect the user and protect the chlorine from UV.

Thanks for your quick and courteous replies! Sounds like I will go dichlor out of the gate to get to 33 ppm then go bleach.

Next questions...if I get to 33 ppm on the CYA and I have ozone and AG+ in the spa, can I just add bleach after each use or does it have to be everyday. My general regimen is to hit a little dichlor and MPS after each use. I balance once a week and hit it with some stain and metal inhibitor. I don't want to be checking the thing every day, but I would go out there every 2-3 days.

[chem geek]

The vast majority of chlorine in the water will be bound to CYA when CYA is present. These combined compounds, called chlorinated cyanurates, are not fast-acting sanitizers nor oxidizers so the bulk of the burden is borne by the active chlorine (hypochlorous acid) that remains. In a spa at 104F with a pH of 7.5, 4 ppm FC and 30 ppm CYA, 84% of the chlorine is bound to CYA, 9% is hypochlorite ion (not an effective sanitizer) and 7% is the active sanitizing form of chlorine, hypochlorous acid. So CYA provides THREE functions: moderating chlorine's strength, acting as a chlorine reservoir, and protecting chlorine from breakdown from the UV in sunlight. You don't need CYA in your situation for the latter function, but you do need it to prevent chlorine from being too strong. You could alternatively have the equivalent amount of chlorine with no CYA which would be 0.6 ppm, but it is very hard to consistently maintain that chlorine level and have it last long enough. You can think of the CYA as an active chlorine buffer, holding most of the chlorine in reserve and releasing it as needed. The actual oxidizing and sanitizing rates (from chemical reactions), however, depends on the instantaneous chlorine concentration and not on the amount that is in the chlorine reservoir (i.e. bound to CYA or as hypochlorite ion).

All of this is well known science that was definitively determined in terms of equilibrium constants back in 1974 as described in the paper at this link. As to why this is not taught by the pool or spa industry, let's just say that anyone who understands the FC/CYA relationship won't be needing to buy algaecide, clarifiers, shocking the pool, excessive pH or TA balancing products, or more expensive (and profitable) stabilized chlorine. There are 20,000 members of The Pool Forum and 10,000 members of Trouble Free Pool who easily and inexpensively maintain their pools using knowledge and facts rather than industry hype (oh, your TDS is too high; oh, you need to raise the TA to get your pH more stable and not rise; oh bleach isn't the same as other chlorine; oh Trichlor tabs don't build up very much CYA; oh, CYA doesn't matter, or you can have up to 200 ppm before it matters; oh, your phosphate levels are high so you have to use a phosphate remover to prevent algae growth; oh, you need to shock the pool every week; etc.).

You may be able to add chlorine after each use if you add enough so that you still measure 1-2 ppm FC for your next soak. If you didn't have an ozonator, then this would be relatively easy to achieve since you would add enough chlorine for the bather load plus enough for the typical 25% per day chlorine loss when the filter is clean. However, with an ozonator you may find the chlorine loss to be higher at 33-50% in which case you'd need to add more chlorine to not run out. You could probably do 2-3 days between soaks, but not a week without really getting the chlorine pretty high.

[mlobitz]

The vast majority of chlorine in the water will be bound to CYA when CYA is present. These combined compounds, called chlorinated cyanurates, are not fast-acting sanitizers nor oxidizers so the bulk of the burden is borne by the active chlorine (hypochlorous acid) that remains. In a spa at 104F with a pH of 7.5, 4 ppm FC and 30 ppm CYA, 84% of the chlorine is bound to CYA, 9% is hypochlorite ion (not an effective sanitizer) and 7% is the active sanitizing form of chlorine, hypochlorous acid. So CYA provides THREE functions: moderating chlorine's strength, acting as a chlorine reservoir, and protecting chlorine from breakdown from the UV in sunlight. You don't need CYA in your situation for the latter function, but you do need it to prevent chlorine from being too strong. You could alternatively have the equivalent amount of chlorine with no CYA which would be 0.6 ppm, but it is very hard to consistently maintain that chlorine level and have it last long enough. You can think of the CYA as an active chlorine buffer, holding most of the chlorine in reserve and releasing it as needed. The actual oxidizing and sanitizing rates (from chemical reactions), however, depends on the instantaneous chlorine concentration and not on the amount that is in the chlorine reservoir (i.e. bound to CYA or as hypochlorite ion).

All of this is well known science that was definitively determined in terms of equilibrium constants back in 1974 as described in the paper at this link. As to why this is not taught by the pool or spa industry, let's just say that anyone who understands the FC/CYA relationship won't be needing to buy algaecide, clarifiers, shocking the pool, excessive pH or TA balancing products, or more expensive (and profitable) stabilized chlorine. There are 20,000 members of The Pool Forum and 10,000 members of Trouble Free Pool who easily and inexpensively maintain their pools using knowledge and facts rather than industry hype (oh, your TDS is too high; oh, you need to raise the TA to get your pH more stable and not rise; oh bleach isn't the same as other chlorine; oh Trichlor tabs don't build up very much CYA; oh, CYA doesn't matter, or you can have up to 200 ppm before it matters; oh, your phosphate levels are high so you have to use a phosphate remover to prevent algae growth; oh, you need to shock the pool every week; etc.).

You may be able to add chlorine after each use if you add enough so that you still measure 1-2 ppm FC for your next soak. If you didn't have an ozonator, then this would be relatively easy to achieve since you would add enough chlorine for the bather load plus enough for the typical 25% per day chlorine loss when the filter is clean. However, with an ozonator you may find the chlorine loss to be higher at 33-50% in which case you'd need to add more chlorine to not run out. You could probably do 2-3 days between soaks, but not a week without really getting the chlorine pretty high.

Excellent! Thanks for the in-depth reply. I really appreciate it! I really enjoy learning how my pool and spa works. I think I've got it just about nailed. It just not that difficult!