If your TC is dropping from 5 to 1 overnight, then you are fighting algae and you need to keep it at 15. You can dilute but I think Ben also says if OTO color goes to deep orange it's close to ten and if it goes to brown it's around 15 (without dilution). Ben can correct me.

In the pictures it looks pretty blue, but that's not reliable. The TC dropping is more indicative of algae.

Looking at your sand filter and your cart, either should EASILY be adequate for your pool and both is over-kill. Plus, you are filtering FIRST with the cart, not the sand. I can see that from the pump, and the way the lines go to the sand filter. So I'm guessing when you put the DE in the skimmer, it clogged the cart. When you pull out the cartridge element and close it up, you should just be using the sand filter.

Again, I'm guessing that you ARE yo-yo-ing because you are not keeping the chlorine at shock level.

Carl