Blah coral colours... any tips?

[High tide]

Do you get good coralline growth? Is that the 48" or 36" fixture? How much food do you feed and how often? What media do you have in your Tom filter?

I agree you need to test your PO4 and NO3 with higher sensitivity test kits. If all your test kits are Hagen I would buy a whole new round of kits. Your parameters could look quite a bit different afterwards.

Provided your bulbs are still young and it's the 48" fixture, I'd say your lighting is adequate. I would swap a fiji purple for a daylight though to raise the PAR.

Feeding your corals could be counterproductive if skimming and waterchanges are not keeping up with the input of nutrients.