During the day on a hot sunny day and especially with water that is that warm, you are gonna lose chlorine. That is normal. But, if you are losing 3ppm overnight, I'd shock the pool.

As far as tiny stuff that you can only see in front of the pool light, that is pretty much true of most people's pools I would suspect. Most likely just dust in the water.

When I test, (I test outside) I just pour the test water on the ground, fill the tester a couple of times with pool water to rinse it and pour that on the ground, too.