Looking at your tank info, looks like you have the following in your tank?
Clown Tang, Blue lip tang,
2 false percula clown
coral beauty angel, flame angel, Blue manderin, sleeper goby, cleaner shirmp, fire shrimp, hermit crab, strawberry crab, purple spot lobster, 10 assorted snails, chocolate chip starfish, porcupine puffer, longnose butterfly. coco worm.
So your tank is 11 weeks old and already has 10 fish in it?
First off, I'd say you're overstocked. But even if you weren't, adding 10 fish within 11 weeks really isn't giving your bacteria time to catch up with your bioload. Normally, a fish a month is a good way to pace yourself. So from that aspect, I'd say your tank is experiencing a cycle trying to play catch up.
Cannister filter media should probably be rinsed out in your old saltwater once a week. You're correct in worrying about the bacteria in it though - with only 30lbs of rock, your filter media will probably end up pulling double duty trying to catch up with the bioload.
I think your low (but not terrible, by any means) pH could also be linked to a cycling issue. When a tank is cycling, the "extra" biological activity that's going on in the tank will tend to drive down the pH. Once the tank matures, the pH will probably come up a bit.
I think with that bioload, you'll be lucky to keep your nitrates below 20. Might want to rethink your stocking list.