I have never aimed to feed zoas and they always grow like a weed for me, well other then 1-2 types. I have had tanks for the last 5+ years and I only just started feeding reefroids and reefchili. I have noticed changes in my lps and softies. I do not think it would be needed for zoas unless you are running a ULN tank. Just my $0.05
I could never get my zoa's to survive so I'd be curious to see what kind of results you get with feeding them. I use reef roids twice a week for my corals and they seem to love it.
I use reefroids and my corals love it, it's true that they dont need to be fed but its an extra for the zoa, but like Tork said it depended on your system.
I almost never spot feed my corals unless they are in bad shape and need a little TLC. I use reef roids and other similar sized foods but with caution. Keep in mind adding foods like this can effect your tank water quality so they need to be used with caution. They need to be slowly ramped up for use as you need to figure out what your system can safely handle or you will cause a massive algae bloom or crash your system. I mainly use detritus mutable days a week as it is nutrient packed and is bacterial sized so pretty much everything will eat it making it the perfect food. I take a turkey baster and blow on the substrate where it touches the rocks. This is the perfect sized food and is a food that will be consumed regularly in the wild. Plus side is if you add mechanical filter media or chemical like a protein skimmer you will be cleaning your tank and feeding your corals. Using detritus also has the benefit of you not adding more food into your system but using up and recycling what you have already in the system. Limiting input and maximizing output from the tank goes a long way to maintain good water quality.
Target feed with a turkey baster weekly with mix of phyto and zoo. I tried at one point to reduce feeding and the coloney started to die off. I resumed the feeding regime and they came back and continue to spread at a good rate.
I could be wrong with my information however. Zoa's that have been "bleached" lose the ability to grow/reproduce based off UV alone. If your zoa's are dieing its possible they have lost all the substance that does the photosynthesis for them. Once that happens you have to feed them manually for them to regain their color (as well as the UV growth)
Not sure any of this applies but when i bought some bleached (cheap) zoa's i was able to get the color back by doing this with reef roids.