I agree with the 'Salt' comments... there is little substitute for a good salt and regular (weekly maybe) water changes. Alternatively, less frequent water changes (perhaps monthly) can result in some of the elements in your tank to become depleted.
When I am keeping up with my my water changes the only thing I add is food (other than Ca and carbonates) and have liked Zeovit's Coral Vitalizer, but it is a bit pricey for me. Recently I have gotten into Reef Snow from Brightwell Aquatics (BA) and am happy with both the product and price.
When I am doing water changes less than weekly I dose KoralColor, also from BA, although most of the other trace element supplements out there will likely be just as good. Also, when my blues/purples are fading, I dose Potassium (K) and notice a big difference after a few days of dosing (the brand probably matters little for this). I have also been messing around with Boron (branded as BoroChrom, also from BA ), and found it really helps with my reds in several, but interestingly not all, of my sps/lps. It is not that expensive and you only add one or two mls a couple of times a week, so a $15 bottle lasts forever.
But, as I said, I don't use any of that stuff when I am doing regular water changes
Dan