I think many people would agree with me that birdsnest is one of the easier SPS corals to grow, but initially I struggled because I neglected to spend money on the single most important factor for artificial reefs: lighting. Changing this one factor has made the biggest improvement in coral health is the quality of the lighting. I bought two Geisemann Marine bulbs and I noticed a HUGE improvement in the colors and growth rates of my corals. Google "Sanjay" and Geisemann and you'll get a great site that evaluates the light quality of different bulbs on the market. It may be a little dated by now, but its worth a check. I also bought a light meter too so I could monitor when the bulbs needs to be replaced.
Obviously, Ca and Kh levels need to be maintained and nutrient levels kept low. Temp stability, H20 changes, drip dosing are all more important in smaller tanks. Attention to these details should help the growth rate of your birdsnest explode. good luck