I have trouble believing that 145lbs of live rock can't accomodate a single Lion Fish and trigger, even though the later is universally agreed as a pig in terms of waste production. The trace ammonia levels and stready presence of nitrate would seem to indicate a handicapped bio filter system if you ask me.
By chance are you not getting good enough water circulation through the LR
? Tried using a power-head or two, like a beefy Aquaclear 802 to punch some circulation through your LR
If your skimmer is placed in a way where it gets really efficient water turnover it shold have no problem keeping up with two good size fish.
Inline filters will work, but they'll require constant changing to keep trapped matter from decaying and causing the same problem. A pound of AC
in an inline filter will keep your water looking pretty though.