Hi Michelle, I add nothing to my tanks to grow the macro. It feeds on naturally occuring nutrients in the water. I like red grape caulerpa, codium, and some caulerpas as long as they are pruned. I would never let the cauplerpa grow too much because it can go sexual. Pretty much any macro is fine for the seahorses. I added the macro immediatley, but my tank had been setup previously as a reef tank for about a year. All I ever fed my tank is mysis shrimp for the seahorses. Hope this helps!