The 11 Most Common Mistakes Made by Saltwater Aquarium Keepers

fishes in a marine aquarium

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No matter what kind of aquarium keeper you are, here is a list of the most common mistakes you may be making. These problems can be avoided if you're aware of them before you start an aquarium.

  • 01 of 11

    Overfeeding Fish and Invertebrates

    How much food should you feed your fish? Do you add more because they always seem hungry? It is important to supply your fish the food they need, but uneaten food just lays on the bottom of the tank, creating ammonia, nitrite and nitrate and overloading the biological filter.

    Not fully understanding the nutritional requirements of their fish, the tendency of many people is to "throw food" at fish in order to fulfill their needs. If the fish are not accepting the food offered, many aquarists will "throw even more" at the fish, thinking that the fish just isn't seeing the food. It is important to feed the correct type of food for the inhabitants in your aquarium and feed them the appropriate amount.

    Most aquarium fish will do well with commercial flake or pelleted food, but you should ask your fish supplier if the fish and invertebrates you are buying for your saltwater aquarium have any special dietary needs. Know what is in the food you are feeding by comparing the nutrients in commercial foods, purchasing only high-quality foods, and feeding only what your fish will consume in three to five minutes per feeding. Feed once or twice per day, depending on the age and species of fish.

  • 02 of 11

    Moving Too Fast

    "Patience" is a requirement for just about anything that you do with a saltwater aquarium. Far too many people report problems after they have put their aquarium together because they are just moving too fast! A high percentage of people do not take the time to read and study up on the fish keeping hobby before getting started. Make sure that you know the requirements of any new species you plan on adding to your saltwater aquarium, and check on their compatibility with the species you already have. When adding fish into your new aquarium, only add a few at a time over the first 4-6 weeks until you have stocked your aquarium. Do not add all of the fish at once.

  • 03 of 11

    Overloading the System

    A problem that goes hand-in-hand with moving too fast is cramming too much livestock and/or live rock into the aquarium all at once, especially in a tank that is not fully cycled or has just completed the nitrogen cycling process.

    Even in a well-established system, placing too many new additions into the tank too quickly can cause new tank syndrome. Slow down! Saltwater aquarium keeping is not a timed event, so take it easy, and work on your patience skills. Let the aquarium water quality get balanced after each new addition before purchasing more fish or invertebrates.

  • 04 of 11

    Inadequate Filtration and Water Circulation

    Having sufficient biological filtration is a primary key to success in keeping a saltwater aquarium. There are a number of filtration methods to choose from, but not making the right filter selection for the bio-load planned for your aquarium can lead to a wide variety of problems. Whether it be ​biological, mechanical, or chemical, it's better to have more filtration, rather than too little for the size of your aquarium.

    This same concept applies to the circulation of the water in the aquarium, as well. The lack of good water flow throughout the system can lead to problems with low DO (dissolved oxygen), the build-up of nuisance algae, the prevention of sedentary animals receiving food, and more. The solution? Add a powerhead or two, or a surge device to improve water movement in the aquarium.

    Continue to 5 of 11 below.
  • 05 of 11

    Misdiagnosing Diseases

    When it comes to diagnosing diseases, saltwater ich is the biggest problem. It is easy to confuse the protozoan parasites Oodinium (Amyloodinium ocellatum - a.k.a. ​marine velvet or coral fish disease) with White Spot Disease (Cryptocaryon irritans). They are similar but two quite different types of saltwater parasites, and each responds to different treatment. It is important to properly diagnose and treat these parasites, as well as other diseases. Seek help from an Aquatic Veterinarian or an experienced aquarist to properly identify and treat fish diseases. The sooner the correct diagnosis and treatment is made, the better chance your fish have for survival.

  • 06 of 11


    Way too often one or more remedies are just thrown at a sick or ailing fish without knowing what is the real problem. Medications should only be used when necessary, and whenever possible treat the fish in a quarantine tank. The most important factor with medications is to use one that is formulated to "target" the specific disease you are dealing with. Always know the exact water volume in the treated aquarium and follow the medication label dosing instructions accurately.

  • 07 of 11

    Purchasing Animals Without Knowing Anything About Them

    It never ceases to amaze us how often people select new additions to their aquarium without knowing what the animals are, and how to care for and feed them. Before purchasing anything, take the time to first obtain information about it. The new addition may not be suited to live with the species already in your aquarium!

    You shouldn't buy on impulse because you like the pretty colors a fish has, how cute or stunning it looks, or for any other "touchy-feely" reason, or if a salesperson can't provide you with critical information you need to know about a particular animal. Be sure there is room enough in your aquarium for the ADULT SIZE of the fish you are interested in, and that it is compatible with the existing species you have.

  • 08 of 11

    Livestock Incompatibility

    Statements like my wrasse ate my hermit crab, my tangs just won't get along, and similar ones are all too frequently heard. Purchasing livestock without knowing whether or not they will peacefully reside with other tank mates can lead to dead or injured animals, as well as stress-related diseases. Use common sense and learn about the compatibility of animals you are considering for your aquarium before putting them together!

    Continue to 9 of 11 below.
  • 09 of 11

    Purchasing Animals in Poor Health

    One of the easiest things to do when selecting a critter is to determine whether or not it is healthy. In a simple phrase, most sick fish don't eat. Before purchasing a fish or other animal, it is best to have a sale's person in a store show you that it is in fact eating.

    Learn how to recognize the symptoms or outward signs of common illnesses so you know what to look for when inspecting livestock to buy. Healthy fish should be actively swimming and have their fins spread out normally, and be interested in food added into the aquarium. Sick fish often will be lethargic, hanging around the top or the bottom of the aquarium, or not schooling with other fish, have fins clamped against their body, and have discoloration or redness to the body and bases of the fins.

  • 10 of 11

    Using a Poor Quality Fresh Water Source

    Although many aquarists do so, choosing to use water straight from the tap or un-purified water of another source to make up saltwater solutions and to top off a tank can lead to many water quality issues in aquariums. Using a water purification filter, buying clean natural seawater, or pre-filtered RO/DI water from a reliable supplier is an investment that will pay for itself in the long run. Unless you have tested your tap water to be sure it is appropriate for mixing with your salt to make sea water, ask your fish retailer what they recommend for salt water aquarium use in your area.

  • 11 of 11

    Lack of Proper Tank Maintenance

    Well-maintained saltwater systems seldom experience high nitrate, bacterial outbreaks, or other water quality issues. To avoid the usual pitfalls with problems in this area of aquarium keeping, set up and follow a regular maintenance routine.

Avoiding these common mistakes will help you become a more successful aquarium keeper.

Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Starting a Freshwater Aquarium. Pet Industry Joint Advisory Council.

  2. Hargrove, Maddy and Hargrove, Mic. Freshwater Aquariums For Dummies. John Wiley & Sons, 2011.

  3. Cryptocaryon Irritans Infections (Marine White Spot Disease) in Fish. University of Florida Institute of Food and Agricultural Sciences.

  4. Gay, Jeremy. The Perfect Aquarium: The Complete Guide to Setting Up and Maintaining an Aquarium. Octopus, 2017.

  5. Zoonoses Associated with Fish (Including Aquarium Fish). Washington State University.