aqua one 620 problem

hey guys i have made the mistake of buying a aqua one 620 tank which my lfs said it will b good enough....well since i am about 4 months into my first saltwater tank i have learnt so much about saltwater aquariums which i now know my tank was a mistake but i don't have the money to just go out and buying another tank so I'm just trying to make this one the best i can.....i am trying to find a protein skimmer for this and it is killing me because of the hood i don't have any coral jus FOWLR everything is good within the parameters but my nitrate is a little bit high like 50ppm.....any help with a protein skimmer would be awesome