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How To Look After Marine Fish (AKA Saltwater Fish): Full Guide

A purple seahorse.

Modern technology has made saltwater aquariums more accessible and straightforward to maintain. Although marine fish tend to be more expensive than freshwater fish and require you to invest more money and time into them, it is most definitely worth it.

A saltwater aquarium can sustain more delicate and unique species and marine life such as:

  • clownfish
  • angelfish
  • seahorses
  • live coral

It can be overwhelming to start your first aquarium. Even experienced fish owners can sometimes feel unsure. However, careful thought, planning, and research will ensure your new saltwater aquarium thrives. In addition, these simple steps will make your experience more convenient and rewarding.

Step 1: Planning Your Aquarium

Planning an aquarium is a great chance to use your imagination and create your ideal tank. Additionally, it enables you to decide what you want to accomplish and on what scale.

Planning can help you determine what you’ll need for your aquarium and avoid wasting money. When planning your new tank, you should decide:

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  • what type of aquarium
  • how big it should be
  • which species of fish

Decide On The Type Of Aquarium

The kind of aquarium you decide on will significantly impact what species of saltwater fish you can accommodate in your tank. Further, the aquarium type determines the range of colors and decorations you can add.

Different tanks and species come with various expenses and costs and require different levels of expertise to maintain them. Different kinds of saltwater aquariums include:

  • Fish Only: If you are only interested in the marine life of a saltwater aquarium, then the fish only tank is ideal for you. This is a very simple and cost-effective aquarium to set up. However, fish only aquariums require a bit more maintenance due to the lack of live rock and other systems that help to control waste. Changing the water in the tank needs to be done more regularly.

  • Fish Only With Live Rock: This brings the focus to the fish in the tank with only a cluster of live rock in the aquarium. Live rock produces bacteria in the aquarium that help maintain the tank. You can add artificial corals and seagrasses to give your aquarium the appearance of a reef.

  • Reef Tanks: These are some of the most iconic and majestic tanks and usually are what people imagine when hearing about saltwater aquariums. However, these are the most expensive and comprehensive tanks because coral dominates them, and coral can be complicated for beginners to understand as they are living organisms. Additional equipment is required to maintain these aquariums.

  • Species-Specific Tank: This is typically made up of one or several species with similar requirements. These species are often aggressive and cannot coexist in the same tank as other species.

Choosing An Aquarium Size

Choosing the correct size for your aquarium will tremendously impact the outcome. However, you must carefully consider your budget when selecting the aquarium size as it will significantly impact the costs of:

  • equipment
  • maintenance
  • tank setup

Larger saltwater tanks are easier to maintain, so we recommend that you start with the largest one you can, considering:

  • Your complete budget.
  • The space you have available for the aquarium.
  • What marine life do you want in the tank?

Choose The Right Fish For Your Tank

The most suitable species or combination for your saltwater aquarium depends on many factors, including:

  1. The type of aquarium you decided on.
  2. The size of your tank.
  3. Your budget.
  4. Your experience with saltwater aquariums.

However, the best fish choices for beginners will be:

  • cost-effective
  • available
  • resilient
  • easy to maintain

Some of the best types of saltwater fish for beginners that meet these criteria include:

  • Damselfish
  • Clownfish
  • Hawkfish
  • Seahorse
An orange and white clown fish swimming in a tank with purple background.
Clownfish are good fish for beginners

Step 2: Setting Up Your Aquarium And Equipment

The fastest and most efficient method would be to purchase a pre-assembled aquarium or have professionals install the aquarium. However, if you decide to make your experience complete by building an aquarium yourself, you will need the following: (these links will take you to the specific products on Amazon; they are products I personally picked out for myself as they are great value and good quality!):

Wet Testing System For Problems

After installing the equipment in the aquarium, you should run a wet test on the system to ensure full functionality and that there is no leakage. Do a wet test before adding:

  • saltwater
  • live rock
  • marine life
  • substrate

To run the wet test:

  1. Ensure that all connections are secured.
  2. Fill the tank with fresh water.
  3. Dry the entire aquarium so you can easily spot any leaks.
  4. Power the pumps one at a time and carefully inspect all connections for leaks.
  5. Carefully check the sump to see if it overflows.
  6. Check that the protein skimmers make bubbles and the pumps used for them are running.

Step 3: Substrate, Saltwater, And Auqascaping

Now you can start cleaning and adding the substrate you have chosen for your tank based on what type of saltwater aquarium you are setting up.

First, you should gently add a thin substrate layer to the bottom of the tank before pouring in the rest to avoid unnecessary scratches.

Next, fill up the tank with saltwater that you can purchase or make yourself by mixing aquarium salt and reverse osmosis de-ionized water.

If you are going to add live rock and have fully cured it, you can add it to the tank along with any other plants, stones, and other decorations. This step is where you can use your imagination and give your aquarium a theme or bring the image you had in your mind to life.

NOTE: Thoroughly rinse all the items before adding them to the tank.

Step 4: Install Aquariums Lighting System

Your tank will have different lighting requirements depending on what type of saltwater aquarium you are setting up.

In addition, the marine life in the aquarium will require at least 8 hours of darkness daily to sleep. You can install a light timer to make this process easier.

However, if you add coral, you need to install reef tank lighting (Amazon link), as coral has more specific lighting requirements than the fish species.

Step 5: Water Cycling And Testing

The ammonia and nitrite in water are toxic to fish. Therefore, before adding any marine life, you must cycle the aquarium for at least a month.

Cycling the aquarium allows bacteria cultures to build up as they act like a biological filter, converting ammonia to nitrites and nitrites to nitrates.

Next, you should test your aquarium water to look for any imbalances in the water chemistry and problems with the general water quality.

Step 6: Introducing Marine Life To The Aquarium

Adding a few snails or hermit crabs to your aquarium can help maintain and minimize algae and waste build-up in the tank.

Next, if your tank supports coral, you can add a few to the tank. From here, you can slowly add more marine life to the tank.

A saltwater fish tank with lots of coral and other marine life.
Coral and live rock can be added to marine aquariums

However, if you add too many fish, coral, or live rock at a time, you risk disrupting the system and restarting the nitrogen cycle, causing catastrophic problems.

Fish are susceptible to changes in water conditions. Therefore, you need to slowly acclimate fish to the water in your tank before adding them to the aquarium. Further, you must closely monitor new fish as they are the most susceptible to parasitic outbreaks caused by stress.

You can adjust fish to the water conditions of the aquarium by:

  1. Place the bag that contains the fish in the aquarium for 15 minutes to match the temperature in the tank.
  2. While ensuring that the bag remains floating, unseal the bag.
  3. Pour about half a cup of water from the tank into the bag every five minutes until the bag is full.
  4. Empty the bag halfway outside of the tank.
  5. Then repeat step 3 until the bag is full again.
  6. Once the bag you filled has settled, you can transfer the fish into the aquarium with a fishnet.
  7. Dispose of the bag and the water that came with the fish.

Carefully monitor new fish for at least 24 hours for any signs of illness. Alternatively, transfer the fish into a quarantine tank for the first day and then move them to the main tank once you are satisfied that the fish is healthy. This process will help protect marine life and reduce diseases in your aquarium.

Step 7: Maintaining Your Aquarium

Once you have set up your aquarium and the marine life starts to take shape, follow a maintenance plan to ensure the health of your aquarium. Contrary to popular belief, maintaining a saltwater aquarium is essentially the same process used to maintain a freshwater aquarium.

FACT: Preserving your aquarium should typically take you only 30 minutes daily.

Daily Tasks To Maintain Your Aquarium

  • Feeding the marine life: Once or twice a day.
  • Test salinity of water: Heated saltwater aquariums cause water in the tank to evaporate, but the salt stays behind, causing the salt in the tank to become more concentrated. Test the salinity of the water daily and regularly top off the tank with heated fresh water to keep the salt levels stable in the aquarium.
  • Test water:  Test the water temperature and chemistry daily, especially if your aquarium is busy cycling.

Weekly Tasks To Maintain Your Aquarium

  • Change the water: Remove and replace about a fifth of the tank’s water with new reverse osmosis de-ionized water or saltwater.
  • Clean filtration system: Inspect the filtration system to ensure water flows freely or clear any debris that restricts the flow and clean filtration media.
  • Clean glass: Cleaning the walls of the aquarium and removing any built-up algae will help prevent it from spreading through the tank.
  • Test water: Test the ammonia, nitrite, nitrate, and pH levels of the water in the aquarium.

Monthly Tasks To Maintain Your Aquarium

  • Maintain filtration system: Inspect and clean the filtration system and replace filtration media.
  • Clean Equipment: Inspect to ensure it works and clean the heater, thermostat, and pumps.
  • Sandbeds: When changing the aquarium water, vacuum and clean the sand bed.
  • Test water: If you are using an electronic probe to test the water of the aquarium, calibrate it monthly.

Differences Between Saltwater Aquariums And Freshwater Aquariums

Saltwater AquariumsFreshwater Aquariums
BenefitsUnique and majestic marine lifeHuge variety and more cost-effective
Typical Beginners FishClownfish, pufferfish, and gobyGuppies, tetras, and goldfish
Marine Life Can IncludeCoral and anemonesSnails
Habitats Can IncludeLive rock and substratePlants
Water NeededAdd a salt mixture to tap waterAdd a dechlorinating agent to tap water
Alternative Equipment RequiredProtein skimmer, coral requires specialized lighting and substrateTank cover, air pump, heater, and thermometer
Set Up Cost$500 to $1000 and fish for around $50Under $50 and fish for as little as $5
Difficulty To MaintainIt requires Investing a bit more money and time but is relatively simpleStraightforward and not very time consuming
A black and white striped fish swimming among purple and green coral.
Saltwater aquariums are beautiful and majestic

Common Mistakes Beginners Make

  • Placing your tank in direct sunlight or right by a window can raise the temperature of the tank, increasing the growth of microalgae and harming the fish.
  • Mixing all sorts of fish without inquiring about the compatibility of the fish.
  • Accidentally poisoning the fish by using a bucket or container that came in contact with chemicals hazardous to the fish.
  • Not putting a lid on the aquarium and losing expensive fish to them trying to escape, as 90% of fish can jump out of the water.
  • Not having an emergency plan during power failures means that your aquarium does not have a heater, filtration system, or air pump, which has been the reason for multiple lost aquariums.


The cost of saltwater aquariums is significantly higher than freshwater aquariums. In addition, maintaining saltwater aquariums requires you to have excellent knowledge and invest more time.

However, a saltwater aquarium will be gratifying and enjoyable to manage. So, if you’re ready for the commitment of a saltwater aquarium, the whole family may enjoy the exceptional beauty that comes with it.

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