It will take you a few times before you get this perfect this is how i found to use the correct amount of shisha.
I normally smoke for no more than an hour so, to find out the correct amount of tobacco i did this.
1. Place a specific amount in the shisha eg 2 mm off the top of bowl.
2. when you have finished smoking your shisha(for me an hour), take the coals off STRAIGHT AWAY to create further burning.
3.Wait for bowl to cool down then check how much unused(wasted ) tobacco there is at the bottam, if there is alot and only the top is burnt, your using to much, so next time you make a bowl decrease the amount.
4. Eventually you will get to the point where you take the tin foil off the bowl to see pretty much all the tobacco burnt with only a slight 2mm layer of coloured wet tobacco at the bottam.
If you shisha tastes of charcoal before you want to stop smoking, then put more tobacco in next time.