The core equipment for a saltwater tank

A saltwater aquarium needs a tank, a way to move and filter the water, lighting, a heater, salt mix, and a way to measure what is in the water. That is the minimum. A 20-gallon tank is the smallest size that stays stable enough for a beginner — smaller tanks swing in temperature and chemistry too fast. You will also need a protein skimmer, which removes waste before it breaks down into ammonia and nitrate. Skimmers are not optional in saltwater the way they sometimes are in freshwater.

The tank itself should be glass or acrylic. Glass is cheaper and does not scratch as easily, but acrylic is lighter and will not shatter if cracked. A 20-gallon tank costs between $30 and $80 depending on material and brand. Larger tanks — 40 gallons, 55 gallons — are actually easier to maintain because the water chemistry changes more slowly, but they cost more upfront and take up more space.

You will also need a stand rated for the weight of a full tank. Water weighs 8.3 pounds per gallon, so a 20-gallon tank full of water, rock, and sand weighs roughly 200 pounds. A stand made for aquariums costs $40 to $150 and is worth the money — a regular furniture stand can collapse.

Key Takeaways

  • A saltwater tank needs a heater, protein skimmer, filter, powerhead, lighting, and a way to test salinity and pH — these are not optional parts you can skip.
  • A 20-gallon tank is the smallest size that holds stable temperature and chemistry; smaller tanks require constant adjustment.
  • You need marine salt mix, not aquarium salt or table salt, and you must mix it with water before adding it to the tank.
  • Testing equipment — a refractometer or hydrometer for salinity, a pH test kit — costs $30 to $60 total and is necessary before you add any fish.
  • Budget $300 to $500 for a complete beginner setup with a 20-gallon tank, or $600 to $1000 if you want room to add corals later.

Filtration and water movement

Saltwater fish produce more waste than freshwater fish, so filtration has to work harder. You need three things working together: a mechanical filter that traps particles, a biological filter that grows bacteria to break down ammonia, and a protein skimmer that removes waste before it decays.

A hang-on-back filter or canister filter handles mechanical and biological filtration. Hang-on-back filters cost $40 to $100 and sit on the rim of the tank — they are straightforward and take up no floor space. Canister filters cost $80 to $200, sit under the tank, and move more water, which is useful if you plan to add corals. For a 20-gallon beginner tank, a hang-on-back filter rated for 200 to 300 gallons per hour is enough.

A protein skimmer removes dissolved waste and foam from the water surface. Skimmers cost $50 to $150 for a tank your size. They look like a tube with an air stone at the bottom — air bubbles rise through the tube, collect waste, and push it into a cup at the top. You empty the cup once or twice a week. Without a skimmer, nitrate builds up faster and you have to do water changes more often.

You also need a powerhead — a small pump that moves water around the tank so nothing sits still. A powerhead costs $20 to $50 and creates the current fish need. One powerhead is enough for a 20-gallon tank.

Heating and lighting

Saltwater fish need stable temperature between 76 and 78 degrees Fahrenheit. A submersible heater rated for your tank size keeps the water warm. A 100-watt heater works for a 20-gallon tank and costs $15 to $30. You should also buy a thermometer — a straightforward stick-on costs $3, or a digital one costs $10 to $20 — so you can check the temperature daily.

Lighting depends on what you want to keep. If you are keeping only fish, any aquarium light works — even a basic LED strip costs $20 to $40. If you want to add corals later, you need stronger lighting. A good LED light for corals costs $80 to $200. For now, start with basic lighting and upgrade later if you decide to add corals.

Testing and water chemistry

Saltwater chemistry is more complex than freshwater. You need to test salinity (the amount of salt in the water), pH (how acidic or basic the water is), and ammonia. You cannot see these things, so you have to measure them.

A refractometer measures salinity and costs $20 to $40. It is more accurate than a hydrometer (a floating glass tube that costs $10 to $15), but both work. Saltwater should stay at 1.020 to 1.025 specific gravity, which is what the refractometer reads. A pH test kit costs $10 to $20 and should show pH between 8.0 and 8.3. An ammonia test kit costs $10 to $15 and should always read zero — if it does not, you have too much waste in the tank.

You do not need to test every day, but you should test before you add any fish, then once a week for the first month, then once every two weeks after that. Once the tank is stable, you can test less often.

Salt mix and water

You need marine salt mix, not aquarium salt or table salt. Marine salt mix contains the minerals fish and corals need — regular salt does not. A bucket of marine salt mix costs $15 to $30 and lasts a long time because you only use it for water changes, not to fill the tank initially.

Mix the salt with water before you add it to the tank. Use tap water if your tap water is clean, or use bottled water if your tap water is hard or has chlorine. Mix the salt and water in a separate bucket with a powerhead or airstone for at least an hour before adding it to the tank. This lets the salt dissolve completely and the temperature stabilize.

For the initial fill, you can mix salt and water in the tank itself, but it takes longer and stirs up the sand. Most people prefer to fill a bucket, mix it, test it, and then pour it in slowly.

Substrate and rock

Saltwater tanks need substrate — the material on the bottom. Live sand costs $1 to $3 per pound and contains bacteria that help filter the water. Dead sand costs less but does not have the bacteria. For a 20-gallon tank, you need about 40 to 60 pounds of sand, which costs $40 to $180 depending on whether you choose live or dead sand.

Live rock costs $3 to $8 per pound and also contains bacteria and small creatures that help the tank stay balanced. You do not need much — 10 to 20 pounds is enough for a 20-gallon tank to start. Live rock costs $30 to $160 for that amount. Dead rock (also called base rock) costs less and works fine if you seed it with a small amount of live rock.

Substrate and rock do two things: they give bacteria a place to live, and they give fish places to hide. Both matter for a healthy tank.

Cycling the tank before adding fish

Before you add any fish, you have to cycle the tank — let bacteria grow in the sand and rock so they can break down fish waste. Cycling takes two to four weeks. During this time, ammonia rises, then nitrite rises, then both drop to zero as bacteria multiply. You test the water every few days to watch this happen.

You can cycle the tank with no fish (fishless cycle) by adding ammonia or fish food, or you can add a few hardy fish and let them produce the ammonia naturally (fish-in cycle). Fishless cycling is slower but safer for the fish. Fish-in cycling is faster but stresses the fish.

Do not skip cycling. If you add fish to uncycled water, ammonia and nitrite will spike and poison the fish. Cycling is the most important step and the one most beginners rush.

Optional but useful items

A quarantine tank is a small separate tank where you keep new fish for two weeks before adding them to the main tank. This prevents disease from spreading. A 10-gallon quarantine tank with basic filter and heater costs $50 to $100 total. It is optional but saves money and stress in the long run.

An auto-feeder costs $15 to $40 and dispenses food on a timer. It is useful if you travel or have an irregular schedule. A basic feeder is reliable; expensive ones are not necessarily better.

A reverse osmosis filter removes chlorine and minerals from tap water, which is useful if your tap water is hard or treated. A small RO filter costs $50 to $100. It is optional if your tap water is already clean.

Frequently Asked Questions

Can I use a freshwater filter in a saltwater tank?

A freshwater filter can move water, but it will not work well without a protein skimmer. Saltwater produces more waste than freshwater, and a skimmer removes that waste before it breaks down into ammonia. A freshwater filter alone will require constant water changes. Use a filter rated for saltwater or add a skimmer to a freshwater filter.

What size tank should I actually start with?

A 20-gallon tank is the smallest that stays stable. Smaller tanks swing in temperature and chemistry too fast and are harder to keep balanced. A 40-gallon breeder tank or 55-gallon tank is easier to maintain and gives you more options for fish and corals, but costs more upfront. Start with 20 gallons if space and budget are tight; go larger if you can.

Do I need to do water changes if I have a good filter?

Yes. A filter removes particles and breaks down ammonia, but it does not remove nitrate, which builds up over time. You should change 20 to 25 percent of the water every two weeks. This removes nitrate and replaces minerals the fish consume. Without water changes, nitrate rises and the tank becomes unhealthy.

How much does a complete beginner setup cost?

A 20-gallon tank with filter, heater, light, skimmer, sand, rock, salt mix, and testing equipment costs $300 to $500. If you add a quarantine tank and better lighting for corals later, budget $600 to $1000 total. Fish cost extra — hardy beginner fish like clownfish or damselfish cost $10 to $30 each.

Can I use tap water or do I need bottled water?

Tap water works if it is clean and not heavily treated with chlorine. If your tap water is hard (high in minerals) or smells like chlorine, use bottled water or a reverse osmosis filter. Mix the water with salt in a separate bucket before adding it to the tank so the salt dissolves completely and the temperature matches the tank.