here is the setup showing the use of alternating photosynthesis to control pH. The palm light comes on at night, the long blue galaxy lights the corals in the day. The thing about these tiny pico tanks is one can easily overdrive the organisms with lighting. A standard daylight 13watt PC bulb will cause both corals and plants to go into 'high' metabolic mode and suck up everything the can from the water. Lack of success with a planted pico betta hex would most likely be attributed to nutrient exhaustion, so I say stay on those Fe and Mg drops. Oh, and add a guppy or dwarf frog for constant nitrogen.
small old reef tank