BTW -by the way
PITA - pain in the bonkus

PH -powerhead
FWIW - for what it's worth
LOL - laugh out loud
FO - fish only
FOWLR - fish only with live rock
MH - metal halide
MV - mercury vapor
PC - power compact [flourescent]
NO3 - nitrate
NO2 - nitrite
PO4 - phosphate
NH3 - ammonia
Ca(Cl)2 - calcium chloride
Ca(OH)2 - calcium hydroxide
kalk - kalkwasser (calcium hydroxide)
HOB - hang on back(stuff that hangs on thetank side vs lets say in the sump)
CL - closed loop [circulation system]