Your water is perfect! You are backwashing correctly. The gray stuff on the bottom is what has settled to the bottom when the pump is off - it is stuff that the clorine has killed - it means that your chlorine is working. Relax and enjoy the water - it seems you have a great take on how to keep up with the pool! Welcome to the forum. As to how to get rid of the stuff at the bottom of the pool without vacuming - get in and stir it up, or brush it in the morning so it goes back into the water and it will eventually filter out.