I currently have a 3 gallon tank with 3 lbs of live rock and live sand, both which have been cured for several months now. Unfortunately, I have been consistently unable to keep macroalgae alive in my tank. I have stocked the tank with Gracilaria Hayi, Gracilaria Parvispora, Caulerpa Prolifera, and Caulerpa Mexicana but all of them have withered away and died slowly after a week. My tank parameters are a temperature of 73 degrees (I plan to stock it with dwarf seahorses), salinity of 1.023, and nitrate and ammonia levels within reasonable bounds. In water changes in weeks past, sometimes I have added new water that have been off by +-0.003 salinity. The tank does not have filtration, only a small powerhead that brings flow to all parts of the tank. I have treated the live rock with panacur to kill off any hydroids. I have an incandescent light with a spectrum of 5000K. What is causing the macroalgae in my tank to die?