there is a difference between ample food for corals and dirty. There are no fully photosynthetic corals they all need to eat. if your tank is so "clean" that there is no food for them they start to Brown out to try and gain more nutrition from photosynthesis. having proper nutrients and properly sized food particles in your tank as plankton will ensure coral health. they all need to eat. it is one of the reasons I dont run mechanical filtration in my tanks as it tends to trap the smaller micron particulates that feed our corals.
the closest to fully photosynthetic coral would be Xenia and they absorb nutrients from the water column as they are not equipped with any actual feeding apparatus.
and just so you know most corals are carnivorous and p[refer zooplankton (with the exception of gorgonians) some consume bacteria some consume smaller pods and such. but having too "clean" a tank isnt actually optimal for coral growth or color.
spot feedintg anycoral that will accept large foods is a great idea, you can even spot feed other corals with (I know some one is going to flame me for this) the juices from frozen foods, and skimmate. I dont reccomend using skimmate for most people its way to easy to OD and cause algae problems, But I do feed all the juices from my frozen meaty foods to my tank as well as liquid skimmate once a week since the liquid part contains tons of bacteria and micro pods. whereas the solids contain a lot of calcium and fatts and oils and other truly hydrophobic substances.
Warning by keeping ample food in your tank like this you do run the risk of algae problems and you need to slowly build up feeding not suddenly increase or you will experience a serious algae problem. keeping tons of macroagaes can help consume the undesirables from heavy feeding, like phosphate and excess nitrate.
avoid flake foods pellets are ok for your fish but really the best is to either purchase frozen foods or make your own. when making your own you can uber puree them to make super fine batches that provide lots of the juices and micro particles that your corals require.
when feeding suspension foods like the juices your average capture for most of your corals is going to be about 2% tyhe rest becomes waste in your tank, so I would advise keeping your skimmer on.
well thats my two cents take it for what its worth.
I get it trust me. I've read and read and hear the same thing. But I'm tellin you that corals don't require 0 trates and phos. I'm assuming that since I have hair algae that my tank has excess nutrients So would that mean its clean, dirty or okay?