High CYA - how much to drain?

[will1874]

[Split by moderator - Please keep questions in your own thread. Thanks, jblizzle]

I'm having a similar problem. Although my CYA is not quite that high. It's north of 120 though.

FC - 13 (I'm keeping it high because of the CYA issue)
CC - 13
pH - 7.4
TA - 90
CH -200
CYA - 130

Pool calculator says replace 67% of the water. Is it as simple as eyeballing the draining process until it "looks" like I got 2/3 of it. I'm worried about damaging the liner. Is there a certain technique to draining this much water?

 

[will1874]

Oops, meant to say CC is 0

 

[Swampwoman]

You might wish to consider a series of partial drains to get to that 67% if you have any concerns about your vinyl liner floating. Alternately, you can use a giant sheet of plastic (eg visqueen) and lay it between the ok'd layer and the new layer as you drain it down/refill. That way you maintain the hydrostatic pressure to avoid problems with the liner.

If your cya is above 120, 67 sounds about right, but if you do partial drains, and can get it down unde 100 you could then maintain the higher chlorine to cya ratio in the interim until you drain again.

 

[duraleigh]

Partial drains of roughly 1/3 are probably the easiest safest way.

YOu can also drain and refill simultaneously if you can match up your drain and fill speeds, the water level will never move. (certainly not as easy as above)

I used to suggest the plastic sheet method, too, as it certainly makes sense.

The problem is that in 9 years of forum experience, there is NO report of ANYONE having performed it. I no longer advise it as the mechanical issues, particularly in a large pool, seem to keep anyone from attempting it.

 

[spidey07]

You can cause problems with the liner if you drain too much. Make sure you have at least a foot of water in the shallow end. Nothing wrong with doing it in batches as mentioned.