The difficulty changed yesterday, the profit have decreased a lot since two week agos with some S9

People! Keep your sanity and watch your long term profits...If you constantly watch daily and weekly profits, you will go nuts! There is just too much variance in this venture for short term happiness.
Right on! Mine on!.
The flip side are things you should watch or do daily.
1) Your miners health, keep a miner stats page up and refresh it to confirm you are maintaining health of all miners.
2) The availability of miners and power supplies to buy.
3) Backup your bitcoin Core wallet daily.