So I've been reading a lot of the information on the relationship of CYA to FC and the recommendations that higher CYA levels may be beneficial to pool owners that get a lot of sun and thus experience a lot of FC degradation. I haven't seen anyone do a chlorine consumption comparison of the different levels, so here it is.
Based on the apparent daily solar degradation rates in the following post(http://www.troublefreepool.com/threa...l=1#post318157), and the FC levels required at varying CYA levels based according to the Chlorine/CYA chart (http://www.troublefreepool.com/threa...rine-CYA-Chart), I put together a spread sheet that shows the amount of FC that needs to be added to the pool daily in order to combat loss due to solar degradation. Note: I added 120 to see where the trend would take me
According to the data provided to me, it looks like running at 50 CYA will use the most chlorine at any given level (min, target, shock, etc.), while running at 20 or 100 (I guesstimated 120 with a value that seems to match the curve) will save you up to 25% of your total chlorine need. Note that percentage of chlorine used daily for a given level are consistent. It scales linearly because the FC/CYA chart scales linearly (within a small margin of error).
Values that require FC higher than 10, and thus are prone to pH testing error are highlighted yellow. My conclusion at this point is that it is better to keep CYA low while correcting pool problems (so that pH can be measured and chlorine levels can fall when desired), but once your pool is well balanced there is very little downside to raising CYA and running higher FC levels (Keep in mind as chem geek noted, that oxidizing power is the same at any given FC/CYA level (min, target, shock)).
Hope this helps some people, I know it helped clarify things in my head. If you have any corrections in my methods, let me know.
Some explanation of the table if it's not clear. CYA is the CYA level and %Daily Loss is the estimated loss in a sunny pool in the middle of summer according to chem geek.
The FC column is the CYA value times the FC percentage at the top (7.3% for Min, 11.4% for Target, etc) which is basically in line with the Chlorine/CYA chart (tweaked to be a little closer to actual values)
The FC Loss column is the amount of FC lost per day. It's the FC value times the %Daily FC Loss value.
% of Max is the percentage of FC Lost versus the worst CYA level (50). 50 is 100% of itself, and they go down from there.