I would go ahead and add the 2nd Maxijet. You can't really count the skimmer in the overall GPH
filtration. I have my 1200's on the corners facing towards the middle of the tank to provide good aeration. 2 of these will give you the flow that you need. 54g X 10 = 540gph would be a good rule of thumb. 2 Maxijet's will offer the perfect solution for this tank, giving you more filtration as you increase your bio load.