Skimmer = only 2 weeks old? Might be the problem. They take a few weeks to break in and work at full capacity. It might be a micro bubble thing for sure. How long has the tank ben running? how long since the filtration cycled?
A picture might help. Also, What kind of skimmer? usually the smaller ones are over rated 2x so you might not be skimming like you think.
On my 120 I ran a TurboFlotor 1000 and it was awesome. Get one of these for your 75 and you'll pull out every last bit of gunk. Smallest salt I had was a 75 and I ran a skimmer that was rated at 120 gallons. It was a Bak-Pak 2 (Dual). Worked great. Tried a lot of others and they all failed to work as advertised.
Crushed coral = bad nitrate problems.
Canister filter = potential nitrate factory.
20lbs of Live rock = 3-4 times more would be a better idea then you can ditch the canister.
UV = waste of money unless used for algae issues only. Then they work great if properly sized.
I used to run all my salt on canisters until I ran into a huge nitrate problem. Upped the live rock and got rid of the canisters and wallah, not more problems.