The sun is a greedy fellow for sure! Between the sun and what the cloudy stuff is you will lose quite a bit during the day. Just look at what you lost overnight. It is not a great bit but that was ONLY what is in the water "eating" your FC so add sun in and..........you get a big lose.
I skimmed over and did not find where any one has talked about adding DE to your sand. Here is a link talking about it. It will help polish your water like you have never seen before.
Pool School - Add DE to a Sand Filter
You can buy the DE at lowes and such. It will come in a big box but does not weigh much. Do you know of anyone that has a pool? They might already have some you can get. It does not take much. I use is off and on and it does not even look like I have used any when I look in my box.
Kim