Need advice please!!

I have a 65 gallon tank. there are a few corals, live rock and 6 fish. Right now I have a HOB filter, a POS skimmer. I tested my water last night and my nitrates were extremely high. I'm planning on doing a 25% water change tonight. I'm thinking my filtration is to blame. I have about $150.00 to invest in something that will help. I'm leaning towards a better skimmer and removing media completely from HOB, need recommendations in my price range. Any other advice would be appreciated!



Thanks!