The Understanding Reef Aquarium Terminology

New to the reef hobby and feeling overwhelmed by the jargon? This comprehensive glossary breaks down every term you'll encounter — from alkalinity to zoanthids.

 

Here is your complete, structured master terminology guide—cleanly organized from beginner → intermediate → advanced → expert-level reefing language. This is formatted for blog publishing, training material, or customer education.

The Ultimate Reef Aquarium Terminology Guide (Complete Edition)

A structured breakdown of reef terminology—from foundational terms to advanced system-level concepts used by experienced reef keepers.

Beginner Level — Core Reefing Terms

Water Chemistry & Parameters

Alk (Alkalinity)
Carbonate hardness; critical for coral skeleton growth.
Typical: 7–9 dKH

Cal (Calcium)
Supports skeletal growth.
Target: 400–450 ppm

Mag (Magnesium)
Stabilizes calcium and alkalinity.
Target: 1250–1350 ppm

SG (Specific Gravity)
Salinity measurement.
Target: 1.025–1.026

Salinity (ppt)
Salt concentration measured in parts per thousand.
Target: ~35 ppt

ppm (Parts Per Million)
Measurement unit for dissolved substances.

pH
Acidity/alkalinity level.
Typical: 7.8–8.3

NH3/NH4 (Ammonia)
Highly toxic; must be 0.

NO2 (Nitrite)
Toxic intermediate; should be 0 after cycle.

NO3 (Nitrate)
End-stage nutrient.
Typical: 2–20 ppm

PO4 (Phosphate)
Controls algae and coral growth.
Typical: 0.02–0.1 ppm

TDS (Total Dissolved Solids)
Measures impurities in water; critical for RO/DI systems.
Target: 0 ppm

Coral Types

SPS – Small Polyp Stony
Small-polyp corals with rigid skeletons, high demand.

LPS – Large Polyp Stony
Fleshy corals with larger polyps, moderate demand.

Soft Corals – No skeleton
Flexible corals without hard calcium structure.

Zoanthids (Zoas) – Colonial polyps

Palythoa (Palys) – Toxic relatives of zoas

Acropora (Acros) – High-demand SPS

Montipora (Monti)
Fast-growing SPS with plating or encrusting forms.

Mushrooms (Corallimorphs)
Hardy soft corals with disc-shaped bodies.

Frag – Coral fragment

Equipment Basics

Sump – Secondary filtration tank

Skimmer – Removes organics

ATO – Auto top-off system

RO/DI – Purified water source

Return Pump
Moves water from sump back to display.

Powerhead – Creates flow

Wavemaker – Programmable flow

Overflow – Drains water to sump

Heater – Maintains temperature stability

Thermometer – Monitors temperature

Lighting Basics

PAR – Light intensity usable by corals

LED – Primary modern lighting

T5 – Even coverage lighting

Actinic – Blue spectrum

Shimmer – Light ripple effect

Kelvin (K Rating)
Color temperature of light output.

Biology & Cycling

Nitrogen Cycle – Ammonia → Nitrite → Nitrate

Live Rock (LR) – Biological filtration base

Cycle – Establishing bacteria

Ammonia Spike – New tank instability

Beneficial Bacteria
Microbes responsible for waste processing.

Hobby Lingo

Reefer – Hobbyist

LFS – Local fish store

WYSIWYG – Exact item shown

Frag Swap – Coral trading event

DT – Display tank

WC – Water change

QT – Quarantine tank

Intermediate Level — Practical Reefing Terms

Chemistry & Stability

dKH – Alkalinity unit

NSW – Natural seawater

ULNS – Ultra low nutrient system

Trace Elements – Minor elements (iodine, iron)

Ionic Balance – Ratio of major ions

Nutrient Export – Removing NO3/PO4

Nutrient Import – Adding nutrients

Parameter Swing – Rapid change (harmful)

Salinity Creep – Gradual salinity increase

Buffering Capacity
Water’s ability to resist pH change.

Filtration & Equipment

Refugium (Fuge) – Macroalgae nutrient export

Chaeto – Common macroalgae

Filter Sock – Mechanical filtration

Roller Mat – Automated filtration

Media Reactor – Runs carbon/GFO

Carbon – Removes toxins

GFO – Phosphate remover

UV Sterilizer – Kills free-floating pathogens

Filter Floss
Disposable mechanical filtration media.

Biomedia
High surface area material for bacteria.

Coral Care

Acclimation – Gradual adjustment

Dip – Pest prevention

Fragging – Coral cutting

Recession – Tissue loss

Bleaching – Loss of zooxanthellae

Zooxanthellae – Symbiotic algae

Photoadaptation – Light adjustment

Polyp Extension (PE) – Coral response indicator

Encrusting
Coral growing across surfaces.

RTN/STN (Rapid/Slow Tissue Necrosis)
Sudden or gradual coral tissue death.

Pests & Issues

GHA – Green hair algae

Aiptasia – Pest anemone

Cyano – Cyanobacteria

Dinos – Dinoflagellates

Detritus – Waste buildup

Flatworms
Common coral pests.

Red Bugs
Acropora-specific parasites.

System Concepts

Tank Maturity – System age stability

Biodiversity – Microfauna diversity

Seeding – Adding bacteria

Ghost Feeding – Feeding empty tank

Dialing In – Fine-tuning system

Bioload
Total biological demand on system.

Advanced Level — High-Level Reefing Concepts

Chemistry & Microbiology

Carbon Dosing – Feeding bacteria to reduce nutrients

C:N:P Ratio – Nutrient balance

DOC – Dissolved organic carbon

POC – Particulate organic carbon

Denitrification – Nitrate → nitrogen gas

Anaerobic Zone – Low oxygen bacteria zone

Nitrification
Ammonia conversion process by aerobic bacteria.

Filtration Systems

Biological Filtration – Bacteria-driven processing

Chemical Filtration – Media-based removal

MarinePure / Siporax – High-surface biomedia

Biofilm – Bacterial layer

Algae Turf Scrubber (ATS) – External algae export

Poly Filter – Broad contaminant removal

Deep Sand Bed (DSB)
Anaerobic filtration through deep substrate.

Lighting & Flow

Photoperiod – Light duration

Spectrum Tuning – Adjusting wavelengths

Hot Spot – High PAR area

Shadowing – Light blockage

Gyre Flow – Circular tank flow

Random Flow – Ideal flow pattern

Turnover Rate – Flow vs tank volume

Laminar vs Turbulent Flow
Types of water movement affecting coral health.

Coral Health

Browning Out – Excess nutrients/low light

Burnt Tips – Alk/light imbalance

Growth Tips – Active SPS growth

Allelopathy – Chemical warfare

Sweepers – Stinging tentacles

Coloration Shift
Changes in coral pigment due to conditions.

Troubleshooting

Mini-Cycle – Temporary instability

Bacterial Bloom – Cloudy water

Precipitation Event – Alk/Ca crash

Alk Burn – Tissue damage from high alk

Parameter Drift
Slow, unnoticed parameter change over time.

Expert Level — System Mastery & Rare Terms

Advanced Chemistry

ORP – Oxidation potential

Refractory Organics – Hard-to-remove compounds

Redfield Ratio – Ideal nutrient ratio

Heterotrophic Bacteria – Carbon consumers

Autotrophic Bacteria – Nitrifiers

Chelation
Binding of metals for biological use.

Advanced Filtration

Fluidized Bed Filter – Moving biomedia

Sulfur Reactor – Nitrate reduction system

Lanthanum Chloride – Chemical PO4 remover

Ozone (O₃) – Water clarity & ORP control

Clarifier – Particle-binding additive

Denitrification Reactor - Dedicated nitrate removal system.

Lighting Science

PAR Map – Light distribution grid

Photoinhibition – Too much light reduces photosynthesis

Light Shock – Sudden exposure stress

DLI (Daily Light Integral) – Total daily light exposure

Diffuse Lighting – Even light spread

Spectral Distribution – –

Flow Dynamics

Turbulent Flow – Chaotic flow (ideal)

Laminar Flow – Straight flow (less ideal)

Boundary Layer – Water layer on coral surface

Shear Stress – Force from flow

Head Pressure – Pump resistance

Manifold System – Multi-device plumbing

Flow Dead Spot – Area with insufficient circulation.

Coral Physiology

Mesenterial Filaments – Digestive attack structures

Symbiont Density – Zooxanthellae concentration

Mucus Production – Defense/cleaning

Tissue Necrosis Line – Visible death boundary

Recovery Margin – Regrowth zone

Calcification Rate – Speed of skeletal growth.

System Failures & Aging

Old Tank Syndrome (OTS) – Long-term imbalance

New Tank Syndrome – Early instability

Tank Syndrome – General decline

Nutrient Imbalance – NO3 vs PO4 mismatch

Bacterial Imbalance – Microbial instability

Clouding Event – Sudden turbidity, bacterial blooms, crashing tank

System Crash – Severe failure resulting in livestock loss.

Disclaimer: This content is intended for educational purposes only. Information may change as reefing practices evolve and new data becomes available. First Due Aquatic Rescue is not responsible for outcomes resulting from the use of this information. Always verify guidance across multiple reputable sources.

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