Should I reduce CYA?

[cjs]

My current CYA reading is 60-70. I've started using bleach to chlorinate, but I am also still using tablets at a reduced level. Not yet ready to commit to full manual mode at this time.

Here are my questions...

Part 1: It looks like manually adding bleach, plus general health issues because of lower chlorine levels, may be a little more reasonable with CYA levels at 30-40 instead of 60-70. Is it worth the effort to reduce CYA to reduce amount of chlorine needed?

Part 2: To reduce CYA, would draining 10% of the pool 5 times have the same effect on CYA as draining 50% of the pool 1 time? (or whatever numbers you would like to use).

Part 3: I understand CYA rises to the top of the pool. Is it always there, even while the pool is circulating, polaris running, etc, or does it get mixed throughout when the pool is running. If it does mix as the pool runs, how soon after you shut it off does the CYA rise to the top? I'm asking because I've been told to reduce CYA you are best to drain from the top. I've done this by connecting my vacuum hose to the skimmer, and shutting off the main drain and the other skimmer, and vacuuming to waste? It is much slower because everything has to come through that one little hose.

Thanks for your feedback.

 

[PaulR]

Part 1:

I don't think the health issues are really different. With higher CYA you must maintain a higher FC to keep the effective sanitization level the same; the total chlorine level on its own isn't all that relevant.

Part 2: To reduce CYA, would draining 10% of the pool 5 times have the same effect on CYA as draining 50% of the pool 1 time?

No, not quite. If you replace 10% of the water, you remove 10% of the original CYA, leaving 90%. If you replace another 10%, you are removing 10% of that remaining 90%, or 9%. And so on. Mathematically, replacing 10% of the water 5 times leaves you with (.9)⁵=.59=59% of the original CYA.

Part 3: I understand CYA rises to the top of the pool.

This is misinformation, the CYA is uniformly distributed throughout the pool.
--paulr

 

[Guest]

My current CYA reading is 60-70. I've started using bleach to chlorinate, but I am also still using tablets at a reduced level. Not yet ready to commit to full manual mode at this time.

Here are my questions...

Part 1: It looks like manually adding bleach, plus general health issues because of lower chlorine levels, may be a little more reasonable with CYA levels at 30-40 instead of 60-70. Is it worth the effort to reduce CYA to reduce amount of chlorine needed?
It will make your maintenance easier and you will need less chlorine but the only real health issue is not having a high enough chlorine level for the CYA level.
Part 2: To reduce CYA, would draining 10% of the pool 5 times have the same effect on CYA as draining 50% of the pool 1 time? (or whatever numbers you would like to use).
No, it would be slightly less but it would also be safer if you do not know what your water table is or you have a fiberglass or vinyl pool.
Part 3: I understand CYA rises to the top of the pool.
Not true. You are talking about something that is dissolved in the water and exists as cyanurate ions. It is equally distributed thorughout just like salt would be when you dissolve it. You cannot lower the CYA faster by taking water from the top (I have also heard that it is mostly on the bottom, btw--another fallicy) than you can remove salt faster from the water by siphoning from a certain depth!