Definitely use a skimmer in the sump since that should give you best results. The fish you stated don't produce much bio BUT shark and lion fish can be fragile to water conditions, so a good skimmer would be your best choice. I use an aqua c ev skimmer and it pulls stuff out of my water that I thought I would only see in sewers. I was having cloudy issues too and my skimmer cleared the water within 24 hours. I tried to keep a lion fish in a tank that had no skimmer and it only lived 2 weeks, and my parameters were are in line. So yeah they are sensitive creatures. A good protein skimmer is your choice as there are many good ones to choose from but from my experience, an aqua c ev is one of the best skimmers for the money.