How long have all those fish been together in your tank and how long has your aquarium been running? A 30 gallon tank for 2 angelfish seems like a bad idea to me. What are the other 4 fish that you have? Also, I hope the 1.04 salinty was a typo, it should be 1.022 to 1.026ish.
On to your question, how often do you do water changes and when you are doing your water changes do you remove any detrius (uneaten food, fish poop, etc)?
What type of powerhead do you have?
A protein skimmer probably wont do much for a tank with little water volume like yours and from what I've read, the lower rated skimmers are junk. If possible and budget allows, get rid of the HOB
filter and get a HOB
sump/refugium. The filter will most likely give you more problems than it is worth.
As for feeding, once every 2 or 3 days is good. I would only feed the brine shrimp as a treat because it really has no nutritional value. Fish are known to get addicted to brine shrimp and not eat the food they should be eating.
Keep feeding the mysis, in fact, its a good idea to feed a variety of foods. Such as feed flakes, wait a few days then feed mysis, wait a few days then feed pellets/flakes again.
Also, are you using rodi
water or tap? How much live rock do you have?
You said that you have your LFS
test the water for you, do they ever tell you the water parameters? I highly recommend getting your own test kits so you can carefully monitor those levels. You can get an API test kit for $17 from petsolutions.com and they are well worth the money.
And welcome to AA!
EDIT: Also wondering if that heater you have is a Marineland Stealth Pro? Those are being recalled, in case you didnt know already =)