The pressure gauge does go to zero when I turn off my pump.

I added another jug of bleach late last night without testing (I didn't see responses to this thread until this morning). I tested late this morning and FC=16 and CC=0. I'm going to add another jug soon to make sure it stays well above 15 (my shock level according to the best guess chart). I've just got to go buy some more. I brushed again this morning and the amount of residue seems a little better, but its still there. I consulted my mother-in-law and we decided the color is a brownish green, somewhere in between. Some areas seem more brown, some more green. Maybe that means its dying but not dead?

I'm also going to go by some DE powder and run the suggested test. How do I tell if my filter needs sand? Do I need to take it apart? Or is there some way to tell without that?

One other thing I may not have mentioned is that my pool leaks fairly significantly through some cracks. I normally top it off every couple of days with a couple inches of water. Today the level was close to bottom of my skimmers. I decided it may filter out more easily if there is less water so I turned off my skimmers and I'm not topping it off. Of course, my pressure dropped to 12 or 13. Is an unwise move? That is, am I better off topping off and running my skimmers or letting it be and turning off my skimmers.

I'll report back after my DE powder test. I'll also start testing late at night and in the early morning to see how much chlorine I'm losing overnight.

One more question... so far I've just been brushing, hoping the skimer and drain would pick up the debris and it would get filtered out. Would I be better off vacuuming? The problem there is that it is so time consuming. Brushing is pretty quick and easy.