I don't know if that grows with no ferts, and even if it does, I need to keep a balance between fish-waste consumers there. I already have 3 fast-growers (and arguably, the java fern seems to have taken the role of 4th fast waste eater)How about some vallis or similar in there Fishblast? That would give them immediate upper-layer cover which might entice them up there..as I recall that stuff spreads out quickly as well - I know my swords of old swam through it a lot!
And yes my hoplo's never stop, constantly up and down to the surface, competing at all levels for food...but then they are juvies unlike your mature fellow
Vallis would probably dry up.
Tzuppy first waits to get first bite at the surface and then dives to the sand and eats everything left over by the swordies.