How to Maintain a Saltwater Aquarium

Marine aquarium

Jessie Sanders

It's no secret that a marine aquarium is more work than a freshwater aquarium. Marine fish require stricter water quality parameters especially regarding pH, temperature and salinity. In order to keep these in the correct range, you will need to have a regular maintenance regimen. The best way to make aquarium maintenance easy is to plan ahead. Setting up your aquarium correctly the first time will make a significant difference to your maintenance routine.

Once your aquarium is up and running, your fish have been added, and you've cruised past the initial cycling period, how do you keep everything swimming smoothly? A set maintenance protocol is necessary to keep your ecosystem healthy. Put it on the calendar and don't skip any tasks!

Regular Water Maintenance Tasks

Checking Salinity/Topping Off: Daily

Heated saltwater aquariums, even with a tight-fitting lid, will lose water to evaporation. When this happens, you will notice the aquarium water salinity increases. This is because when the water leaves your tank, the salt stays behind, becoming more concentrated. To correct this, you will need to add heated FRESHWATER on a regular basis. It will feel very odd at first, but this will keep your salinity stable. Make sure your salinity stays in the correct range using a hydrometer or refractometer.

Changing Water: Weekly

For the first few months of your saltwater aquarium, you will need to keep a strict water change schedule. When you first set up an aquarium, it will take some time for it to cycle and all your water quality levels to balance. This is the balance between the new fish you just added, any invertebrates, such as corals or shrimp, and your biological filtration. Once your tank is fully cycled, you may still have a few hiccups over the first 6-8 months. Regular water changes will help keep these from becoming a bigger problem later. This is especially true if you plan to keep adding live elements, such as fish or live rock, and are still finessing your equipment setup.

When performing a water change, use a gravel or sand siphon to get into the deeper layers of your substrate. This will not hurt the bacteria living in the substrate! If you can, move your décor or live rock and vacuum underneath. You’d be surprised how much debris can pile up these elements. Be cautious not to disturb any bottom dwellers! You can make new piles of substrate for any burrowing fish, but be sure not to suck them up or squish them during gravel vacuuming and cleaning.

Maintaining Filtration: Weekly

Part of your water change regimen should be inspecting your filter media. No matter what kind of filter media you choose, it should allow water to flow freely and not get plugged from lots of debris. You never want to replace all your filter media at the same time, or you will lose the beneficial bacteria that make up the biological filter. You can rinse and reuse most filter media, unless it is falling apart. After you have collected your waste water from your water change, use that water to rinse your filtration media. Never rinse your filter media in freshwater, or you may lose the beneficial bacteria it contains. Once you have removed the larger debris, be sure to wipe out the filter container and replace the media. It will not look or smell clean–that’s the point! You want to keep your biological filtration bacteria in their place.

Making Saltwater: As Needed

If you are keeping saltwater fish, you will need a way to collect or make saltwater. If you live close to a beach and plan on collecting water, make sure it has been properly tested and is allowed by your local laws. It is strongly recommended that you sterilize “wild” water for at least 24 hours with a UV sterilizer so you don’t bring in any dangerous or nuisance pathogens from the wild.

If you don’t have access to a supply of ready-made seawater, you will have to make your own. You can start with tap, well or RO water. If you are using tap or well water, be sure it is tested prior to making your saltwater. Use a dechlorinator chemical to remove chlorine or chloramine from tap water. Using Reverse Osmosis (RO) filtered water is best for mixing a salt solution. There are many different salt mixes you can use, and they will be specific to an all-fish saltwater aquarium or one for fish and corals. Corals require more carbonate and phosphate to make their rocky homes and will need these coral-specific salt mixes. When you are first getting started with saltwater, it is recommended that you start with fish only. Adding corals will require more specialized aquarium, light, water flow and saltwater requirements.

Scrubing Algae: Weekly

Fish + water = algae; there’s no way around it. If you have corals, their need for strong lights will often make algae problems worse. Scrubbing your glass or acrylic aquarium walls with an appropriate scrubber on a regular basis will help remove the algae build up. If you have a severe algae problem, check your water quality. High levels of phosphate and nitrate will cause algae blooms.

Checking Water Quality: Daily/Weekly/Monthly

Maintaining good water quality is essential to ALL aquariums, both fresh and saltwater. A good saltwater aquarium plan will allow your system to be set up correctly with proper filtration. When you are first starting out and your aquarium is still cycling, you will need to check your water chemistry daily. This is especially critical if you are cycling your tank with fish. Once you have made it past the initial cycling period, you can scale back to checking your water chemistry weekly, but only if you are not in the process of adding more fish, invertebrates or equipment. If you are still adding elements, keep testing daily. Waiting too long between testing when you are still developing the nitrogen cycle can be disastrous if you do not catch problems early. Once you are done adding or making changes to your system, give it four weeks to finish cycling, then you can start cutting back on your testing.

Saltwater fish more strict requirements for the water pH (acid-base balance) than most freshwater fish. It is critical to maintain a consistent pH for any saltwater aquarium system. Most salt mixes will include enough carbonate buffers to keep your pH stable, but it is still important to check the pH level regularly.

Replace your liquid-based test kit yearly. The “expiration dates” printed on the packages are only for the stores that sell them. Once you open the bottles, you have one year to use the liquid. If you are using an electronic probe, be sure to calibrate it at least once a month following the manufacturer’s instructions.

Checking Water Temperature: Daily

The only water parameter you must always test daily is temperature. Do not rely on sticky, external thermometers. Invest a few dollars in a submerged thermometer or a few more for a digital one. Check it daily to make sure your heaters are functioning correctly. Tropical saltwater fish are not happy when cold and will easily sicken and die.

Regular Fish Maintenance Tasks

Feeding Fish: Daily

Many saltwater aquariums will have a variety of fish and invertebrate species that may have different dietary requirements. Before you even purchase your fish, research which diets would be best for them. Some marine fish are very picky eaters and if you are not prepared, your investment will be lost.

Most marine fish feedings are best done as a broadcast. This describes scattering the food over a large area of the water surface, focusing on areas with increased water flow, such as powerheads or filter outflows. This will decrease any potential competition, especially with aggressive fish species, and allow everyone to get their fair share. You may need to target feed any fish with specific diets, such as obligate carnivores or herbivores who are not interested in the general diet. Sessile invertebrates, such as corals, clams and anemones will need food too! Most tropical marine fish will require twice daily feeding. Remember, in the wild, these fish are constantly hunting for food and do not do well with lengthy fasting periods. If you are going to be out of town, these fish do better with a trained human feeder, rather than an automated one. However, persons not familiar with feeding fish have a tendency to overfeed them, which can quickly contribute to poor water quality and fish loss!

Checking Fish and Invertebrates: Daily

In order to make sure your fish are all healthy, you must watch your aquarium carefully every day. Use it as your daily meditation time to watch all your fish. It may take some time to see them all appear, and you might have to search out those that like to hide. Feeding time is a great time to evaluate your fishes’ appearance and behavior. Marine invertebrates, corals included, should also be evaluated every day. If you have an animal of concern, contact your local aquatic veterinarian for more assistance.

If you are out of town, make sure whoever is watching your fish knows how many you have and their individual quirks. Do you have any jawfish who like to bury themselves? Do you have any damselfish that prefer one tiny cave? Do you have any hawkfish that will hide under a mushroom coral when anything disturbs their tank? What about your invertebrates? Some owners will leave pictures of their individual fish with their favorite hiding places, so fish-sitters have a good idea of who is in their charge.

Quarantining Fish: As Needed

All fish owners will benefit from having a hospital or quarantine tank at the ready. This does not have to be as fancy as your main system, but a smaller tank with complete filtration will suffice. Fish in hospital systems are usually more stressed out, so give them appropriate places to hide. A hospital/quarantine tank does not have to be up and running constantly, but it is recommended to place your hospital filter media in the main aquarium filter to get it up and running quickly. After your hospital tank is no longer in use, thoroughly clean your media before re-using it. Any fish showing active signs of disease should be moved to quarantine if you can catch them with low stress. Absolutely all new additions, be they fish or invertebrate, must complete a thorough quarantine period prior to being added to the main aquarium.