Welcome to AA.
Did you rinse the gravel? Also to add, gravel isn't well suited for salwater aquarium because of the amount of gunk it traps under it. Sand it much better and easier to care for. Will cause you less issues in the long run with water quality.
I'm unsure what you mean from "water was cloudy behind the filter". Does your filter cartridge just need rinsed? Did you rinse the liverock when you got it?
Live in the Western MD/West Virginia/DC Metro Area?
Join our very active regional forum Here
Like the advice someone just gave you? Add to their reputation! Click on the balance icon underneath their username and let them know.