There is an other problem now. The graph displays 2.1-2.2k hashrate instead 2.56k.
It displays more real hashrate before i set static diff. So i dont understand anything now.
What kind of diff did you set? I set +100000 for my GPU miners, but they are 8*rx480 each, so about 6+ KH/s. You probably need lower diff for your 2.5 KH/s miners, try 30-40k. With 100k you just might not find enough shares of that difficulty and thus your reported by the pool hashrate is lower than your cards are actually capable of.