Resource Center Menu

Marine FOWLR (Fish Only With Live Rock) Setup Guide and Care Sheet

Developed with and approved by a qualified veterinarian.

Marine FOWLR Aquarium


Marine FOWLR tanks are a great way to bring a piece of the ocean into your home. Live rock adds a more natural appearance and additional biologic filtration to a marine aquarium. These tanks have easier upkeep and require less testing and supplementation than a reef tank. In a FOWLR tank, you can keep many fish who would generally consume corals and invertebrates, making it a popular setup choice for more aggressive fish like puffers and triggerfish.

Table of Contents


Habitat size

Although FOWLR tanks can be set up in any size, you will want to know how many and what type of fish you are looking to keep in the aquarium. It is recommended to select the largest tank you can afford and fit safely in your home, as many marine species can get very large as they mature. The larger the tank, the more stable the water quality and conditions will be, and the easier it will be to keep your fish happy and healthy.


The tank should be placed away from direct sunlight, windows, outside doors, heat vents and air conditioners. Rapid changes in water temperatures are extremely stressful for all fish—especially for marine life. Keep in mind that water weighs approximately 8 pounds per gallon, so a 55-gallon tank will weigh over 460 pounds! Be sure your floor will support this amount of weight, and a tank stand is used to ensure the tank is stable and level. If you rent your home, be sure to check your lease. Some apartments and condos limit the size of aquariums allowed. Also, check for electrical outlets, most marine tanks will need access to at least four sockets.

Using live rock and sand to kickstart the nitrogen cycle in your tank is highly recommended—though live rock and live sand are not technically alive. “Live” refers to the bacteria, algae, sponges, crustaceans and other invertebrates who live on and within the rock and sand. By utilizing these live components, it will effectively shorten your tank’s cycling period.

Initial setup

Start by rinsing out the tank with warm water to get rid of any dust or debris inside. Position the aquarium stand into place, making sure it's level; adjust if needed. If you don't have access to a carpenter's level, place the tank on the stand and fill with 1–2 inches of water. Check to see that the water is an even distance from the top of the stand on all four sides; an unbalanced aquarium can be extremely hazardous. Placing a tank on an uneven or tilted surface increases the risk that the tank will tip over, crack or leak. A proper stand designed for an aquarium is important; using anything other than a manufactured tank stand may void your tank's warranty.

Make sure there is enough space between the wall and the back of the aquarium to adequately fit filters and cords and allow easy access for maintenance.

If using an aquarium background, affix the background to the tank prior to filling with water and placing the aquarium against the wall.

Fill the tank approximately 1/3 full. Carefully dry off the bottom edge of the tank and stand. Now check for leaks. Look for water beading up on the bottom edge or running down the sides of the stand. If the tank leaks, empty it and return it to the store for a replacement. You can attempt to fix it, but repairing a leaky tank is difficult, with no guarantee of success.

Filter and skimmer

Set up your filter and protein skimmer, if utilizing, according to the manufacturer's directions. Do not plug your filter or protein skimmer in at this time.

Add substrate

Thoroughly rinse the substrate and décor before placing it into the aquarium. (A kitchen colander works well but be sure to disinfect it before using it for food preparation.) If utilizing live sand, rinse it in a small bucket of premixed saltwater and discard the dirty saltwater after rinsing. Do not add live sand to the aquarium until after the salt has been added.

Fill the tank

If no leaks have been noted, continue to fill the tank with water, leaving a couple of inches from the top to allow for water displacement when the live rock is added. To protect the décor and aquascaping, as well as to prevent splashing, place a small saucer or bowl into the tank and pour the water directly onto that. Recheck the tank for leaks.

Add the appropriate amount of water conditioner or additive to the tank.

Heater and thermometer

Place the heater into the tank but do not plug it in yet. The best place for the heater depends on the type of heater. Non-submersible clip-on heaters that must hang vertically in the tank should be placed as close to the outflow of the filter as possible. Submersible heaters should be placed as close as possible to the inflow of the filter. These placements allow the heated water to be better dispersed throughout the tank. Recheck the aquarium again for leaks.

Install the thermometer according to the manufacturer's directions. The thermometer should be on the opposite end of the tank from the heater in a position that is easy to check. Place the hood and light (if applicable) onto the tank. Plug in the filter and light. Make sure the cords running from the tank touch the ground before looping back up to the plug. This is called a “drip loop” and prevents water from running down the cord into your electrical socket.

Wait 20 minutes, then plug in your heater and protein skimmer. Top off your water level, if needed. Following the instructions included with the heater, adjust your heater to keep your tank between 74 and 80°F.

Adding salt, live sand and live rock

Finish by slowly adding commercial marine salt until you get a specific gravity reading of around 1.020, testing with the hydrometer or refractometer. Your goal is a specific gravity of 1.020 to 1.025

for a fish only with live rock marine aquarium. It may take up to 24 hours for the specific gravity level to stabilize, so wait before making your final specific gravity adjustments. After the specific gravity has reached 1.020 you can add the live rock and live sand. Finish adding additional water to complete filling the aquarium if needed.

Stabilizing period

Your marine aquarium is now set up and running, but don't rush off to buy fish just yet. You need to wait until the temperature and specific gravity have remained stable for at least 24 to 48 hours. This allows the atmospheric gases in the water to dissipate and salt to fully dissolve, and lets you ensure your heater is working correctly. Don't be panicked if your water becomes cloudy; this is natural, but wait until the cloudiness dissipates before adding fish.

If the water temperature and specific gravity levels have remained stable for at least 24–48 hours and the cloudiness has disappeared, you are now ready to begin the cycling process of your new tank. Additives can assist with speeding up the nitrogen cycle. Please refer to the Nitrogen Cycle Care Sheet for your next steps.

Ongoing maintenance and care

Water maintenance

Maintaining great water quality with regular water changes and adequate filtration is important to help keep your marine FOWLR tank healthy.

  • Daily: Check filter, water temperature and other equipment.
  • Weekly: Test water quality at least once a week, and scrape algae growth as needed.
  • Weekly to monthly: Change 10–25% of the total volume of water every 2–4 weeks, or as needed; change filter media monthly.

Cleaning your habitat

CAUTION: Never use soap or any chemicals on any elements of a fish tank. A 50/50 mixture of water and vinegar works very well to clean the exterior of the aquarium and any components needing a refresh. Soap and other chemicals can be harmful to aquatic life.


Tank health / troubleshooting

Issue Causes Suggested Action
Cloudy Water Tank cycling (bacteria bloom), substrate residue, organics and heavy minerals in tap water Perform a 10–25% water change and siphon the substrate, removing residual debris; water clarifier additive may help; reverse osmosis water filter can remove contaminates found in tap water; add nitrifying bacteria additive
Green water Algae bloom, too much light (direct sunlight), excessive nutrients, overfeeding, overstocked aquarium Reduce photo period and block any direct sunlight; increase water change frequency; reduce feeding; ultraviolet filtration can assist with destroying algae cells
pH fluctuations Buildup of organic material and debris, increased levels of CO2 Perform a 10–25% water change; reduce feeding; increase water circulation and surface agitation
Ammonia spike Insufficient nitrifying bacteria, too many fish Perform a 10–25% water change but do not siphon the substrate; reduce feeding, add a nitrifying bacteria additive.

Additional care sheets

Notes and sources

Ask a Pet Care Center associate about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases such as atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life or habitat contents to help prevent the potential spread of disease.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing or caring for aquatic life and should consider not having aquatic life as a pet. Go to for more information about aquatic life and disease.

The information on this care sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.