some more additions:
Some Common Internet Chat Acronyms:
BBL = be back later
BRB = be right back
BTW = by the way
FAQ = frequently asked questions
FWIW = for what it's worth
FYI = for your information
HTH = hope that helps
IMO/IMHO = in my opinion/in my humble opinion
IOW = in other words
ITA = I totally agree
JK = just kidding
LMAO = laughs my *** off
LOL = laughing out loud
OMG = oh my God
PITA = pain in the ***
ROFL = rolling on the floor laughing
TTYL = talk to you later
TY = thank you
WTH = what the heck/hell
YMMV = your mileage may vary
Aquarium-Specific Acronyms:
DIY = do-it-yourself (projects)
FW = freshwater
GF = goldfish
GPH = gallons per hour
HITH = hole-in-the-head disease
HOB = hang-on-the-back (filter, equipment)
LFS/LPS = local fish store/local pet store (also see below under "Reef-specific")
NTD = neon tetra disease
QT = quarantine
RTBS = red tailed black shark
SAE/CAE = siamese algae eater/chinese algae eater
SFF = siamese fighting fish
SW = saltwater
TB = tiger barb OR fish tuberculosis (depends on context)
UGF = undergravel filter
Water Quality-Specific Technical Acronyms:
DOC = dissolved organic compounds
GH = general hardness
KH = carbonate hardness (german K spelling)
PPM = parts per million
RO/DI = reverse osmosis/deionization
TDS = total dissolved solutes
TWP = tap water purification
Light-Specific Technical Acronyms:
CRI = color rendering index
MH = metal halide
NO = normal output
PC = power compact
VHO = very high output
WPG = watts per gallon
More Reef/Marine-Specific Acronyms:
DSB = deep sand bed
FO = fish-only (tank)
FOWLR = fish-only with live rock (tank)
LPS= large polyps stony (coral)
LR = live rock
LS = live sand
RTN = rapid tissue necrosis
SG = specific gravity
SPS = small polyps stony (coral)