CYA / FC Clarification

[DUAR4612]

Hello,
New to the site. Thank you for all the great info. Having a teal, cloudy pool issue. I am preparing to do SLAM and am in the process of buying what i need. (Test kit is ordered) I have a SWCG and on the Cl / CYA chart it say that CYA of 60 will have a target Slam Shock FC of 24. It also says 60 is not recommended. However, in the SLAM guidelines it says "SLAMing an outdoor pool is most effective when CYA is around 30 to 40. Below 30 you lose too much chlorine to sunlight" I am assuming this only applies to non SWCG pools. Correct?

In other words for a SWCG pool my CYA should be 70 and the Shock FC target should be 28. Right? Thanks

 

[woodyp]

Do NOT raise it! SLAM it where you are now cause you won't be using the SWG any way. Welcome.

 

[Richard320]

When performing a SLAM, you're using bleach as the chlorine source, therefore, treat it as a chlorine pool.

If your CYA is above 30, don't add any more until after the SLAM.
If your CYA is above 60, you might consider replacing some water before attempting to SLAM.
If you have no CYA, get it to 30 for the SLAM, then raise it after. But one caveat: If you had CYA last year but now you don't, you could have a major problem and there is an intermediate step that should be taken before the SLAM. Post back if that's the case. Otherwise, don;t worry about what it is.

 

[RobertScalchi]

Richard320. "But one caveat: If you had CYA last year but now you don't, you could have a major problem and there is an intermediate step that should be taken before the SLAM. Post back if that's the case."

Other than water dilution from spring rain and winter snowfall. Can you kindly elaborate the scenario that if CYA fell from last season, what is the major problem you are eluding to?

 

[DUAR4612]

CYA is 30, when I get the kit I'll get rolling and post my progress. My CYA did not drop to zero from last year, so I'm glad I don't have any other issues. Thanks

 

[Richard320]

Richard320. "But one caveat: If you had CYA last year but now you don't, you could have a major problem and there is an intermediate step that should be taken before the SLAM. Post back if that's the case."

Other than water dilution from spring rain and winter snowfall. Can you kindly elaborate the scenario that if CYA fell from last season, what is the major problem you are eluding to?

CYA degrading into Ammonia.

 

[Agent99]

My CYA is usually around 40 for the summer and closing. Upon opening the next year, my CYA is almost always zero.

I'm curious to hear more about the deal with ammonia.

 

[Richard320]

My CYA is usually around 40 for the summer and closing. Upon opening the next year, my CYA is almost always zero.

I'm curious to hear more about the deal with ammonia.

Use the search box and you'll learn more than you ever cared to know about it. It's probably not an issue for you. It seems to be more prevalent where pools actually close (not just get too cold to get in) and temperatures drop below freezing.

You're going to lose 3-5% CYA every month just by natural decay.