Saltwater aquarium supplies differ from freshwater supplies in two significant ways: the equipment requirements are more demanding, and the water chemistry requires ongoing active management. You'll need a protein skimmer, a quality refractometer to measure salinity, RO/DI water or a unit to make it, marine salt mix, and lighting capable of supporting photosynthetic life if you want corals. The baseline investment for a functional marine fish-only tank starts around $500 to $700. A reef tank capable of keeping demanding corals starts at $1,000 and can go much higher.
That sounds expensive because it is, relative to freshwater. But the payoff is a tank that's genuinely unlike anything you can create in freshwater. The color, diversity of life forms (fish, corals, invertebrates), and visual complexity of a well-maintained reef tank is one of the most impressive things you can keep in your home. Understanding what supplies you actually need, and why, is the first step to doing it right and avoiding expensive mistakes. Here's a complete breakdown.
Water: The Foundation of Saltwater Aquariums
Freshwater aquariums can use conditioned tap water. Marine tanks, especially reef tanks, cannot. Tap water contains chlorine, chloramines, phosphates, nitrates, heavy metals, and trace minerals that are tolerable in freshwater but problematic in saltwater, where even small nutrient loads cause algae explosions and harm corals.
RO/DI Water
Reverse osmosis with deionization (RO/DI) removes up to 99 percent of dissolved solids from tap water, producing nearly pure water suitable for marine systems. You can:
- Buy RO/DI water from a local fish store (usually $0.50 to $1.00 per gallon)
- Buy it from grocery store water machines ($0.35 to $0.50 per gallon)
- Make it yourself with a home RO/DI unit
For tanks over 40 gallons, a home RO/DI unit pays for itself within six months to a year compared to buying water. The BRS 4-Stage RO/DI System and the LiquaGen 5-Stage RO/DI unit are both popular options in the $150 to $250 range.
Marine Salt Mix
You mix RO/DI water with marine salt mix to create saltwater. Popular brands include Instant Ocean Sea Salt, Reef Crystals (which adds elevated calcium and magnesium for reef tanks), Red Sea Coral Pro Salt (higher in calcium, magnesium, and alkalinity for demanding SPS corals), and Brightwell Aquatics NeoMarine.
For fish-only systems, standard Instant Ocean or Coralife Scientific Grade Marine Salt is fine and less expensive. For reef tanks with stony corals, a salt mix with elevated major elements like Red Sea Coral Pro makes parameter maintenance easier.
Mix at a ratio to achieve a specific gravity of 1.024 to 1.026 for reef tanks and 1.020 to 1.025 for fish-only systems.
Refractometer
A refractometer measures salinity by refracting light through a sample of tank water. The Milwaukee MA887 Salinity Refractometer and the Hanna Marine Refractometer are two reliable options. Avoid cheap swing-arm hydrometers, which are notoriously inaccurate. At $25 to $40, a quality refractometer is worth buying.
Filtration for Marine Tanks
Marine filtration typically involves a combination of a protein skimmer, live rock (which provides biological filtration), and possibly mechanical filtration through a sump with filter socks or a refugium.
Protein Skimmers
A protein skimmer is standard equipment for marine tanks. It removes dissolved organic compounds before they break down into ammonia and nitrate. Our best aquarium equipment guide covers specific skimmer models in detail, but here's the key point: buy a skimmer rated for 1.5 to 2 times your actual tank volume.
For a 75-gallon system, look for skimmers rated to 120 to 150 gallons. The Reef Octopus Classic 202-S, the Bubble Magus Curve 5, and the Aqua Remora are common recommendations at different price points.
Live Rock and Biological Filtration
Live rock is rock covered in beneficial bacteria, coralline algae, and tiny invertebrates. It provides most of the biological filtration in a reef system. A common guideline is 1 to 1.5 pounds per gallon of tank volume, though modern porous aquaculture rock provides more bacterial surface area per pound than natural rock, so less is needed.
Dry rock (no living organisms) is increasingly popular because it doesn't risk introducing pests like aiptasia anemones or pest algae. You can seed dry rock with bottled bacteria and it becomes biologically active over six to eight weeks.
Sumps
A sump is a secondary tank plumbed beneath the display tank, usually housing the protein skimmer, heater, and other equipment. Sumps increase total water volume (which helps buffer parameter swings), hide equipment from the display, and provide a refuge for a refugium with chaeto algae that exports nutrients.
Many reef hobbyists use the Trigger Systems Ruby or Orca series sumps, or build their own from standard glass tanks by adding baffles.
Lighting for Reef Tanks
This is where saltwater aquarium costs diverge most dramatically from freshwater.
Fish-Only Systems
For a fish-only saltwater tank (FOWLR: fish only with live rock), standard LED lighting in the 10,000K to 20,000K color temperature range provides the blue-white spectrum that gives marine tanks their characteristic look. Budget options like the Nicrew 24/7 Marine LED work for FOWLR systems.
Reef Tank Lighting
Corals (particularly stony corals like Acropora and Montipora) require high-intensity lighting in specific spectrum ranges to photosynthesize and maintain their symbiotic zooxanthellae. The common unit of measure is PAR (photosynthetically active radiation).
Soft corals and LPS corals (brain corals, Hammer corals, torches) do well at 50 to 150 PAR. SPS corals (Acropora, Montipora) typically need 200 to 400+ PAR.
Reliable reef tank lights include: - AI Hydra 32 HD: Popular mid-range LED for tanks up to 24 inches wide. Around $400. - Radion XR15 G6: High-quality Ecotech Marine fixture. Around $500 to $600. - Kessil A360X: Single pendant design known for shimmer and color mixing. Around $500. - Aqua Illumination Prime 16 HD: Compact and affordable for smaller reef tanks. Around $180 to $220.
Water Testing and Chemistry
Saltwater reef tanks require testing for more parameters than freshwater setups.
Essential tests: Ammonia, nitrite, nitrate, pH, alkalinity (dKH), calcium, and magnesium. For reef tanks, alkalinity, calcium, and magnesium are as important as ammonia because they're consumed by corals building their skeletons.
The Salifert test kits are widely regarded as more accurate than API saltwater kits for the reef parameters. Red Sea Pro kits are another reliable option. For hobbyists who want automated and continuous monitoring, the Neptune Apex and GHL ProfiLux are complete controller systems that monitor pH, temperature, salinity, and ORP automatically.
Target parameters for reef tanks: - Temperature: 76 to 78 degrees Fahrenheit - Salinity: 1.025 to 1.026 specific gravity - pH: 8.1 to 8.3 - Alkalinity: 8 to 11 dKH - Calcium: 380 to 450 ppm - Magnesium: 1,250 to 1,350 ppm - Nitrate: Below 10 ppm for most corals, below 5 ppm for sensitive SPS
Two-Part and Calcium Reactors
As corals grow, they consume calcium and alkalinity from the water. You must replenish these elements.
Two-part dosing: Adding equal volumes of calcium solution and alkalinity solution (typically baking soda based). BRS 2-Part and Brightwell Aquatics Reef Code A+B are standard products. Good for tanks under 200 gallons.
Kalkwasser: Adding calcium hydroxide to the auto top-off reservoir replaces evaporated water while simultaneously dosing calcium and alkalinity. Simpler than two-part for stable, moderate-growth systems.
Calcium reactors: Dissolved CO2 breaks down calcium carbonate media inside a reactor, releasing calcium and alkalinity into the tank automatically. The most stable long-term solution for high-coral-density systems. Initial cost is $200 to $600+ for the reactor and CO2 equipment, but operating costs are low.
Our top aquarium equipment guide covers these supplementation systems with specific product comparisons.
Water Flow and Circulation
Marine tanks need substantial water movement to simulate reef conditions. Corals need flow to remove waste from their surfaces and deliver nutrients. Fish in high-flow reef systems are typically healthier than in stagnant conditions.
Aim for total tank circulation of 20 to 40 times the tank volume per hour for reef tanks. A 75-gallon reef needs 1,500 to 3,000 GPH of total water movement.
Powerheads and wavemakers deliver this flow. The Jebao OW and SW series, the Tunze Turbelle Nanostream 6055, and the Ecotech Marine Vortech MP series are all commonly used. The Ecotech Vortechs are the premium option with wireless control and battery backup, which allows the wavemakers to keep running during a power outage.
FAQ
How long does it take to cycle a saltwater tank? With live rock and bottled bacteria, the nitrogen cycle typically completes in two to four weeks. With dry rock only and bottled bacteria, expect four to eight weeks. Test ammonia and nitrite regularly. Only add fish when both read zero.
Do I need a sump for a saltwater tank? No, but it helps significantly. A sump increases total water volume, hides equipment, and makes maintenance easier. Many successful reef tanks run without sumps using HOB protein skimmers and internal circulation. If your tank design allows it, a sump is worth adding.
What's the cheapest way to start a saltwater tank? A fish-only or fish-only-with-live-rock (FOWLR) setup is the least expensive entry point. Skip the high-end lighting (corals need it, fish don't), use a standard HOB protein skimmer, and stock hardy marine fish like clownfish, damselfish, and chromis. A functional 30-gallon FOWLR setup can be built for $400 to $600 total.
Can I use tap water in a pinch? For a short-term emergency top-off, conditioned tap water is less damaging than letting salinity climb dramatically. For regular use, no. Tap water's dissolved solids accumulate in a marine system over time and cause ongoing algae and water quality problems that are difficult to resolve.
The Three Things That Matter Most
If you're starting a saltwater tank, prioritize in this order: first, your water source (RO/DI is non-negotiable for reef tanks), second, your protein skimmer (buy one sized generously for your tank volume), and third, stability in all parameters (temperature, salinity, pH, and alkalinity). A saltwater tank with clean water, adequate nutrient export, and stable parameters will thrive even if other equipment is modest. Chasing premium equipment while neglecting water quality and parameter stability produces poor results every time.