When i connect to waffle pool i lost 20% of my hashrate !
Is that mean the waffpool take 20% of hasrates for itself ?
You're lucky, it usually takes 25%.NO, wafflepool takes nothing more than the 2% fee. Most of the times when hashrate is incorrectly displayed it's a problem on the user's end.
Hashrate as reported by pools is ALWAYS an estimate. The pool doesn't know your real hashrate, it can only estimate it based on the shares you submit.
So, your hashrate as reported on a pool:
1. Is subject to variance (will drift up and down)
2. May be lower if you are getting hardware errors or encountering other issues.