General

ASW = Artificial Salt Water
BB = Barebottom (no substrate)
BR = Base Rock
BS = Baking Soda (sodium bicarbonate)
CC = Crushed Coral
CL = Closed Loop
CUC = Cleanup Crew
DI = Deionization
DOC = Dissolved Organic Carbon
DSB = Deep Sand Bed
EC = End Cap (light)
FO = Fish Only
FOWLR = Fish Only With Live Rock
FTS = Full Tank Shot (photography)
HO = High Output (light)
HOB = Hang On Back
HOT = Hang On Tank
LFS = Local Fish Store
LNS = Low Nutrient System
LPS = Large Polyp Stony (coral)
LR = Live Rock
LS = Live Sand
MH = Metal Halide
NSW = Natural Salt Water
NO = Normal Output (light)
ORP = Oxygen Reduction Potential
PAR = Photosynthetically Active Radiation
PC = Power Compact (light)
PH = Powerhead
RSM = Red Sea Max (aquarium)
QT = Quarantine Tank
REDOX = Reduction / Oxidation
RO = Reverse Osmosis
RODI = Reverse Osmosis / Deionization
RTN = Rapid Tissue Necrosis (coral)
SB = Sandbed
SG = Specific Gravity
SPS = Small Polyp Stony (coral)
SSB = Shallow Sand Bed
STN = Slow Tissue Necrosis (coral)
TDS = Total Dissolved Solids
ULN = Ultra Low Nutrients
ULNS = Ultra Low Nutrient System
UV = Ultra Violet (light)
VHO = Very High Output (light)
WH = Wiring Harness (light)
WC = Water Change

Chemical
AC = Activated Carbon
KH = Alkalinity
CA = Calcium
GAC = Granular Activated Carbon
MG = Magnesium
PH = Acidity/Alkalinity measurement
PO4 = Phosphate
NH3 = Ammonia
NO2 = Nitrite
NO3 = Nitrate

Livestock
BS = Brittlestar
BTA = Bubble Tip Anemone
CB = Coral Beauty
CBB = Copper Band Butterfly
CBS = Coral Banded Shrimp
GBTA = Green Bubble Tip Anemone
GSP = Green Star Polyps
LMB = Lawn Mower Blenny
LTA = Long Tentacle Anemone
PBT = Powder Blue Tang
RBTA = Rose Bulb Tip Anemone