What sort of skimmer are you running on the tank Milad and is there any irregular food going into the tank? I'm almost positive your problem stems from the peninsula set up, I had the same thing happen on my 170g.
Situating all your power-heads on one wall in the tank causes a great deal of water to be sucked to those locations, if your powerheads are lower in the tank this in turn causes a lack of flow on the surface. If you increase your return pump and get randomized side to side flow this will fix the problem.
My 2 MP40W's run on anti-sync long pulse mode creating flow on one side of the tank for about 25 seconds and then the flow switches to the other side, this clears the surface very well.
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