CYA HELP

[Etek14]

How does CYA affect the chlorine process, My CYA level got too high from using the tub of trichlor I had left instead of bleach. I drained enough to get it to 70 (I know this is still a bit high), I shocked pool last night with 3 jugs of 182 oz from Sams. I showed fc at 20 after 30 minutes in pool. This morning I had fc of 11. Does a high CYA cause it to show less FC than you would have at a lower CYA or will ALgae reduce the FC level faster at a higher CYA. I'm trying to understand why I used to get home and my chlorine test showed I still had some FC but now since my CYA level got higher and I quit using trichlor and switched to bleach the sun and/or algae is eating my chlorine for dinner. I'm like everyone else trying to find that point for my pool where It's the cheapest to maintain.

PH 7.5
TA 100
CYA 70
CC <.5

 

[Guest]

You didn't say but is your pool green? When you have algae in your pool chlorine is consumed very quickly no matter where your CYA is. If you lost 9 ppm FC overnight you are killing algae. With a higher CYA you need a higher FC to achieve the same level of killing power but the proportional loss of chlorine (percentage of the chlorine lost killing the algae) will be about the same. If your CYA was lower the amount of chlorine you would need would be lower and you would have lost a smaller amount overnight BUT you still would have lost about half the chlorine you put in overnight just like now. The chlorine is being used up killing algae. You will not lose chlorine overnight from sunlight. The higher the CYA the less you lose chlorine from sunlight but the less active the chlorine is in the water so you need more of it.

Also, when you were using trichlor you were constantly feeding chlorine into the pool with either a floater or feeder. With bleach you are dosing with chlorine at intervals of one or two days (unless you are killing algae, then it's more often) so the chlorine level will fluctuate some (Unless you have a SWG or some sort of automatic dosing systm like a peristaltic pump or the Liquidator).
Most people find that they need to add a small amount of bleach daily or every other day and that it takes less than 5 minutes to test and adjust the levels so it's not a lot of work.

It is DEFINITELY more cost effective than using trichlor and the associated needed chemicals. There have been several cost comparisons done in this forum and others and bleach always wins.

Hope this explains it.

 

[Etek14]

Waterbear, thanks for the feedback. I'm definately sold on the BBB method. Don't like adding one thing to counter ill effects caused by the other etc and racking up CYA. My pool is not green at all but I know you can still have Algae. I have full sun except very early and late in the day. If it takes more chlorine the higher the CYA level but less chlorine the lower the CYA and you have full sun i'm guessing the 50 CYA recommended level is a happy medium or I need to find my ideal level over time?

 

[PaulR]

I think of it this way: The CYA acts to hold some chlorine in reserve. The rest of the chlorine is your active sanitizer, but is also vulnerable to sunlight. The sum of these is your FC. The more CYA you have, the higher fraction of your FC is in reserve. That's why higher CYA levels provide better protection from the sun, but also require higher FC levels to maintain sanitization--and MUCH higher FC levels to fight off algae.

The 30-50 recommendation is a balance between amount of chlorine lost "naturally" through sunlight and the levels of chlorine needed to fight off algae or whatever. What works for your pool may lie within these recommendations, or it might not. Particularly in very sunny areas or southern latitudes, people tend toward the upper end of that range or even a bit higher. If you're at 70 now and don't have algae or any other problem, then you can probably live with it for this season and let natural dilution from rain and backwashing let the CYA fall slowly over time.
--paulr

 

[Guest]

What PaulR said!
Very good advice!

 

[Etek14]

Thanks guys, I'm assuming the higher FC level for sanitizing and much higher for killing Algae still equates to much less bleach bought at the store than if you had no CYA. Out of curiousity how bad is ratio of chlorine loss with typical full sun and NO CC's or Algae and no CYA?

 

[PaulR]

I remember chem geek quoting something like 35 minutes to lose half your FC in full (midday) sun, zero CYA, and nothing else using it up.

CYA is a good thing, in moderation!
--paulr

 

[chem geek]

Not only that, but with no CYA in the water the chlorine is TOO strong unless you try and maintain a very low level such as 0.1 ppm FC and that becomes impractical since it gets used up locally too quickly. So even in indoor pools without sunlight, a small amount of CYA can be helpful to moderate chlorine's strength. It doesn't take a very high level of "active" chlorine to kill pathogens nor inhibit algae growth so a lower level means a slower oxidation of your swimsuits, skin and hair and that's a good thing.