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Common Saltwater Aquarium Mistakes And How To Avoid Them

by Brian Dunleavy
Common Saltwater Aquarium Mistakes And How To Avoid Them


Starting your first saltwater aquarium is no walk in the park, and you may experience some slip-ups along the way. But do not worry, as it is normal for the odd thing to go wrong here and there. 

Luckily for you, we are here to tell you what may have gone wrong and how you can avoid these mistakes in the future. 

10 Saltwater Aquarium Mistakes 

With advances in technology, keeping an epic saltwater aquarium is less challenging than it used to be, however, this doesn’t mean it’s going to be extremely easy. Owning an aquarium means maintaining a stable environment for your livestock. 

However, this isn’t the only challenge you will face, so we have an overview of 10 common saltwater aquarium mistakes and how you can avoid them. 

#1: Buying A Tank That Is Too Small

Let’s start with one of the most common saltwater aquarium mistakes, starting with a tank that is too small. While a small tank may sound like a good idea or an easier approach to the hobby, this is a mistake. 

Small aquarium setups are some of the most challenging environments to keep stable because of the limited space.

The best approach is to plan ahead. Think about what type of saltwater aquarium you want to keep, whether it be a fish-only aquarium, fish-only with rock aquarium, or the ultimate goal of setting up a reef tank. 

The size of your tank will also depend on how many fish you want to buy. Your budget will also play a part in this, and if you cannot afford at least a 29-gallon tank, it is best to wait until you can. Trust me, it will save a headache further down the line!

At Reefco Aquariums, we recommend buying a standard 55 or 75-gallon tank for your first aquarium. A larger tank gives you more flexibility in terms of what you can add, plus it makes it easier to find the right equipment needed to maintain a healthy environment for your fish. 

#2: Overfeeding

Overfeeding is typically the easiest mistake for newbie hobbyists. 

When you see your fish begging for food, you may think you are starving them. But, don't get us wrong, it’s important to feed your fish the amount they need to be healthy. 

However, overfeeding your fish leads to two issues:

  • Negatively affecting your fish’s long-term health
  • Water quality issues

  • The general “rule of thumb” is to feed your fish once or twice a day. The best guideline is to go off how much food your fish can consume in one to two minutes. Uneaten food will sink to the bottom, causing spikes in ammonia, which are lethal to fish. 

    Most saltwater aquarium fish will be happy with a commercial flake or pelleted food, but always check with your local fish store (LFS) if your fish have any dietary requirements.

    #3: Overstocking Your Aquarium

    We have all been there. We see those inspirational reef tanks, wanting to cram in as much livestock to create that mini-ocean look all at once. But wait, as overstocking your aquarium will overload your system.

    Now, this is the essential part!

    Before you add any livestock or live rocks, you must fully cycle your aquarium to complete the nitrogen cycling process. 

    Yet, even with a well-established system, placing too much livestock into your aquarium can cause the following issues:

    • Decreased dissolved oxygen levels
    • Spikes in ammonia
    • Spike in nutrients, leading to algal blooms
    • Increased stress with fish from lack of space
    • Overstocked aquariums are more costly to maintain
    • Too many fish, believe it or not, are not as enjoyable to watch

    So, take it slow and remember to quarantine your fish before adding them to the aquarium. Also, give new additions time to acclimate before adding another. 

    #4: Incorrectly Topping Up Evaporated Water

    Over time, your aquarium water levels will drop due to evaporation, which requires you to top up the water to keep the water level consistent. 

    Mixing up new salt water, and adding it to the top of the tank, is a common mistake. For those that skipped chemistry class, adding salt water to your aquarium will increase the salinity levels after a few weeks or months, crashing the system. Usually, by this time, the increase in salinity has already started to cause issues for your livestock. 

    Always use fresh water when your aquarium water needs topping up. 

    #5: Poor Water Filtration And Circulation

    Maintaining sufficient filtration is key to successfully keeping a saltwater aquarium. Lack of filtration and circulation quickly causes issues with your water parameters and fish’s health

    Nowadays, there are many options to choose from when selecting aquarium filtration. We highly recommend adding the following:

    • Powerhead, or even two 
    • Wavemaker
    • Filters and water pumps
    • Air pump and air stone

    #6: Poor/Lack Of Tank Maintenance 

    In addition to maintaining sufficient filtration, your aquarium requires additional tank maintenance. Aquariums suffering from poor or lack of tank maintenance will face issues such as high nitrate, bacteria and algae outbreaks, and other water quality issues

    Part of keeping a saltwater aquarium is to keep up with your water changes, frequently test the water, and check that your equipment is working, replacing faulty items. 

    #7: Misdiagnosing Diseases

    Unfortunately, fish and coral diseases are not uncommon in the aquarium hobby, and many go misdiagnosed. For example, marine Ich is the biggest problem reefers face, but it is often confused with marine velvet because of similar symptoms. 

    It is critical to diagnose fish and coral diseases properly, so that you can provide the best treatment. If you are unsure what to look for, check out our article on common fish diseases and how to treat them.

    #8: Purchasing Fish/Corals In Poor Health

    Buying fish and corals in poor health almost goes hand-in-hand with misdiagnosing diseases. Before purchasing livestock, inspect it to determine if it is healthy or not. 

    Recognize the typical symptoms of unhealthy fish:

    • Frayed fins/tail
    • Skin sores
    • Fuzzy/white spots on the skin and mouth
    • Growths on skin. 
    • Cotton-like “hair” on the skin
    • Uneaten food
    • Rapid breathing
    • Lethargy

    #9: Overuse Of Medication

    After noticing your fish are sick, you will want to treat them. Overmedication is very common when people do not know how to treat fish diseases. Over medicating fish can lead to loss of their protective slime coat, and problems with your biological filter.

    Fish medications should only be used when necessary, and ideally in a quarantine tank. After identifying the illness, select the correct form of treatment, and always follow the dosage guidelines.

    #10: Ignoring Compatibility

    Finally, let’s address compatibility issues. 

    Fish do not always get along. Buying livestock without knowing their compatibility with others could lead to injured or dead animals. 

    This is why it is important to research what fish will happily live with others inside your saltwater aquarium. 


    Mistakes will happen along the way, but avoiding the above mistakes will help you become a better aquarium keeper. 

    If you need help with aquarium maintenance or reefing supplies, contact the Reefco team. We are always happy to assist you with any aspect of your aquarium setup!

    by Brian Dunleavy