Quote from: shadyshahin on August 12, 2016, 11:29:55 PM

is the difficulty increase every day? so the money or BTC i get every day become low couz the difficulty increase?

Bitcoin difficulty is retargeting every 2016 blocks, which is about two weeks. You could also expect every 13 days the difficulty is increased by 7% percent (thus you mine 7% less coins everyday after this), but the difficulty sometimes go down, sometimes goes up but the long term trend is upward so far. Check https://bitcoinwisdom.com/bitcoin/difficulty
to get the graphs of past difficulty changes. The upward long term trend is clearly visible, thats why you should put in mining calculators +5% to +10% difficulty increase after every two week retarget period to get better idea how many Bitcoins you can mine with your S9.