How much vertical room do larger fahaka's reallly make use of? Might have to move my 120g (6x2x2) to the 2nd level of an old house and am paranoid about the tank weight. If I filled it to 18 inches (90 gallons?) would that be sufficient? It's only 4" right now but the only time I see him swim up to the surface is when it wants food. Mostly lateral movement at the substrate level since i've got him. Thoughts? Thanks!