David,
Here are a couple of other things to consider in your target FC = 5, CYA of 40 and min FC = 3. [note, anyone of the above can critique my points bc now I've done a lot of reading and could be dangerous]
1. How much sun does your pool receive? Does the house block it in the morning, afternoon or neither? The more sun, the more consumption of CL, so adding at night does not use CL
2. Do you have trees around or anything else that puts organics into the pool, esp if it's windy. The more organics, the more consumption of CL..wind usually blows more in the day, so more chance of leaves in your pool during the day. - also, if your skimmer bowls are full w leaves, remove them ASAP...
3. How does your pool get CL and what type is it? Any of the tablets or non liquid Chlorines [di-trichlor's ] add CYA to your pool, thus inevitably it will take more CL to protect your water as noted by Matt above.
4. water temps - the cooler the water, the less CL used, also, the higher the pool activity or spa used and water heated, the greater the usage of CL
Every pool/surroundings/environment elements are diff...you need to consider all of the above and build that into your target FC, thus impacting your Min FC.
Regards, tstex