CYA reduction arithmetic; CYA decay?

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J

Jo Jesty

0
Aug 6, 2014
7
Mt Sinai, NY
What an excellent site!

It's been obvious to me for a while that my CYA is way too high, through using dichlor for ages. Only through reading this site did I find that out. I just ordered a kit with a CYA test, but already I'm sure: adding yet more dichlor or even hypo barely registers chlorine on the Cl test, and the algae won't die! No problem with pH: very close to 7.2 with small monthly doses of carbonate. So, two suggestions/questions (for comment please).

1) Reducing the CYA (don't know the level yet, probably way over 100)... I doubt draining is possible for most vinyl pools, so I did the step-wise arithmetic for my pool, 16 x 32 rectangular. Pumping out a manageable 15 inches comes to about 5K gal. After draining, refill to skimmer. Repeating this three times--at the cost of 15K gal of fresh water--will reduce the concn of dissolved stuff by about 55%. Possibly more if you pump only from the drain and point the refill hose to the surface. When I do it and have the CYA numbers I'll let you know how it goes.

2) What's the consensus on optimum CYA for reasonable Cl buffering: around 30, or less?

3) Assuming I use mostly sodium hypochlorite (bleach) to shock and chlorinate after reducing the CYA, what acid should I use to neutralize that: dry bisulfate or muriatic (sulfuric)?

4) Does CYA ever go away/degrade, or am I stuck with it? (Of course every time I backwash some water goes out the drain, and more is lost on closing and reopening the pool. All of that is replaced by rain or from the hose, probably about 5K gal per year.)

5) I'm probably missing something else important...please inform!

Many thanks

JJ
 
Welcome to the forum!

Answers in red below....

Jo Jesty said:
What an excellent site!

It's been obvious to me for a while that my CYA is way too high, through using dichlor for ages. Only through reading this site did I find that out. I just ordered a kit with a CYA test, but already I'm sure: adding yet more dichlor or even hypo barely registers chlorine on the Cl test, and the algae won't die! No problem with pH: very close to 7.2 with small monthly doses of carbonate. So, two suggestions/questions (for comment please).

1) Reducing the CYA (don't know the level yet, probably way over 100)... I doubt draining is possible for most vinyl pools, so I did the step-wise arithmetic for my pool, 16 x 32 rectangular. Pumping out a manageable 15 inches comes to about 5K gal. After draining, refill to skimmer. Repeating this three times--at the cost of 15K gal of fresh water--will reduce the concn of dissolved stuff by about 55%. Possibly more if you pump only from the drain and point the refill hose to the surface. When I do it and have the CYA numbers I'll let you know how it goes. Remember that CYA is only a part of total dissolved solids.

2) What's the consensus on optimum CYA for reasonable Cl buffering: around 30, or less? 30-50 for manually chlorinated pools.

3) Assuming I use mostly sodium hypochlorite (bleach) to shock and chlorinate after reducing the CYA, what acid should I use to neutralize that: dry bisulfate or muriatic (sulfuric)? Adding bleach is a net pH neutral event.

4) Does CYA ever go away/degrade, or am I stuck with it? (Of course every time I backwash some water goes out the drain, and more is lost on closing and reopening the pool. All of that is replaced by rain or from the hose, probably about 5K gal per year.) No, CYA only leaves the pool when water (with CYA in it) goes overboard, usually in the methods you referenced.

5) I'm probably missing something else important...please inform!

Many thanks

JJ
Click to expand...
 
:wave: Welcome to TFP!!!

Just to add to the above answer for #4: The CYA does degrade, but very slowly. Like 3-5ppm per month. There are also times over the winter when a bacteria will convert the CYA often to ammonia which requires a lot of chlorine to get rid of, but the CYA will be gone.

Does sound like you need to replace water and get the CYA down. You should leave at least a foot of water in the shallow end.
Then you will need to follow the ShockLevelAndMAINTAIN Process to clear up the pool.
 
Thank you SO much. I will follow up when I've gone thru the partial draining and shock etc. BTW, with regular brushing (green matter on the floor sucked down the drain into the filter) and vacuuming (old little Arneson, super gadget), the pool is just slightly cloudy, perfectly swimmable. But it's near-daily work to keep it that way when the water is much over 80F. JJ
 
1. leaving a foot in the shallow end of my vinyl pool 5 times to get my cya from over 350 to 50 was entirely possible. Just do a diluted sample to find out how many times depending on your results you may have to perform the process.
 
If you decide to replace some water it is better to fill in with a hose close to the deep end of the pool and discard the excess water from a skimmer. Usually the fresh weater is colder and will say at the bottom of the pool while the last year water is warmer and will stay closer to the surface. The new and the old water will not mix if you do not tun the pool pump with the filtation system. In this way you discard only the water containing high concentration of cya.
 
All turned out well, thanks to the excellent advice. By Taylor's kit, CYA was about 130! Pumping out about 15K gal, I got it down to about 40 (reading that black dot depends a lot on lighting!). I pumped down to about 1 ft, like TimerGuy, and added gently into the shallow end from the hose. Now I can easily get a reasonable FC, 1-2 ppm, using 12% hypochlorite ($25 for 4 gal case at the pool store, not bad), 2-3 cups a day. If I dopn't use the pool, I still have algae a bit at the end of the week--I'm sure when I vacuum half of it just goes straight thru the filter and back in the pool--and I'm thinking of replacing my sand with glass, which seems to be the best-recommended alternative for actually catching algae (like my old, defunct, DE filter used to do so well). And Smykowski was right about the pH: on adding a shock, it rises; but then it settles back down again as the hypochlorite makes chlorine. Thanks again.
 
If you still have algae in the pool a SLAM is in order. Once you eradicate all of it as long as you keep the FC above the minimum for your CYA level it should not return.

Sand replacement is very seldom necessary. It is possible you have channeling in your sand filter and need to do a deep cleaning of the sand to fix it.
 
Correct me if I'm wrong, but I don't think I've seen how (what test kit?)You're using to test your pool. If you don't have one, you really need to get an adequate test kit such as the TF-100 or Taylor k-2006-- both of which can be ordered at TFkits.net.
Whoops I just found you used a Taylor for your cya. I hope it's the k-2006 so you have a fas-dpd chlorine test.
 

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