I recently bought an S4 from bit main on their latest deal. I decided to host it with umisoo and have to pay 150 $ /month for the power usage. I found lot of good reviews on f2pool and decided to use them.
I have now been mining for 1 week and my average hash rate is ~2 Ghash. My average payout is 0.02400611 BTC. That is equal to 0,7 BT per month. Which with the rate of today is equal to ~260 $. So that means that my profit is 110 $.
Note that I didn't calculate with the difficulty increase. With this small calculation you can easily see that it will take me at least 8 months of time to get my invested money back = 850 $.
Am I doing something wrong or this is how it is ? Should I change pool ?
Only thing I see wrong with your above post is the 2GH portion (2TH). No, your figures are pretty much spot on insofar as daily profitability using a pool.
You might get modest gains switching over to say Discus Fish or ghash.io but yes, your looking at 8 months to ROI and that is assuming difficulty remains static (hint: it won't).
Start watching to see what the resell value of your hardware is in the next 3-4 months as well. If you think the ever-shrinking # of satoshi's your generating per day is depressing, just wait a few months and then see what your unit is selling for on e-bay.
Welcome to bitcoin mining. Get out while you still can!