Correct water pars. Correct filtration. Correct amount of light. Correct placement in tank. Correct fish in your set up. Correct tempature. Correct Feeding. Correct amount of flow and correct amount of stability. Once you achieve that, you will get the correct amount of of growth.
With that said...
Water pars.
Ammonia, nitrite, nitrate should be 0ppm. Nitrate is ok though for 0-20ppm, It happens. Phosphate .04ppm and under. Calcium 380-550ppm. Magnesium 1200-1500ppm. Alkalinity 6-11. Salinity .023-.026.
Filtration.
Good skimmer. Simple set up not alot of pads that will hold nitrates. Optional fuge if have room. Filter sock is great choice. Optional but Reactor with some carbon and GFO. Keep it simple. Simple is key.
light.
light is obviously mandatory, but optional on type. T5 I notice personally has best growth. LEDs are not needed, but will really make the colors pop. Metal halide would work, but placement low is mandatory. Power compact is enough, but colors will not pop as much and really nice zoas and Palys will seem dull.
Placement & flow
Placement is huge. Depending on where placement is, hi or low means light amount, left and right will change flow rate. Zoas and Palys usually like macerate lighting, so depending on light matters where placement of high and low should be. High watts/par/lumen means placement is all around anywhere. Low amounts means place higher in set up. Flow is huge too. I notice personally my magicians, super sonics, and other higher end zoas like alot of flow. My supersonic zoas like the skirts to be bashed around every now and then. Then again, some of my more common basic zoas like just simple deep water reds or greens like moderate flow. If it seems happy, it's happy. If not fully opening or seems unhappy, then move not just over an inch, but maybe higher or lower as well depending on how it reacts.
Fish.
Reef safe fish only. No fish that may pick on or both zoas. Or even swim low on rock set up and constantly like to touch them. My wrasse and clowns constantly run my zoas and close them.
Tempature.
A nice stable 77-80 degrees.
Food.
Correct feeding is obvious as well. All corals want something different. Zoas usually planktons. Phytoplankton is what many uses use.
Stability.
Tank needs to be stable of everything I said. No fluctuating of tempature or water pars or salinity. Keep it all stable.
With all that achieved... Your zoa heads, or any corals you purchase for here on out should be happy, grow well, and thrive.