When the TA test changes (in one or two drops) from green to Red / intense pink you're there. 80 sounds pretty good.
I meant puttng it in the pool skimmer - it then goes through the pipe, through the pump then onto the sand. As far "as all at once" - slowly into the skimmer, you don't want a big chunk to clog your pipes or pump.
if you've only one run period a day, best to add the dichlor at the beginning of the pump run. I wouldn't pour it in the skimmer if the pump is not running and neither should you.
I've used a nylon stocking doubled over - some people use tube socks.
So... FC 4.5 on a sunny day - loss of 2.5 today. Another 2.5 puts you below your minimum. I'd dose with a pound of dichlor. You'll need to add Borax after that to lift pH.