Blah coral colours... any tips?

[High tide]

No problem, glad to offer some advice.
Just the filter floss, cleaned or replaced regularly, and carbon changed periodically are good enough. Bio balls and sintered glass are designed for fish only systems where NO3 is not as big a deal and much better than NH3 and NO2. They have no place in a reef tank. It would help to put a Chemi-pure Elite in there to bring down your PO4 and NO3 when needed.