Another advantage of soil is that all the organics in it make for a trace element synch. Soil tanks do not need fertilizers or trace elements added becouse of this. You can grow swordplants in 1watt/gallon light this way. The only problem is you will have too many plant spikes to grow all the plants. With the marine substrate under the gravel there is also a lot of locked carbon the plants take in roots too so less dissolved carbon is need in tank from co2.