Common Beginner Mistakes with Marine Aquariums

After being asked about, and reading about, many situations were hobbyist experience problems with their first marine aquariums, (as well as thinking back to my first marine aquarium) you could attribute almost all of these difficulties to the below list of the most common mistakes people can make with their first marine aquarium.

These are not listed in any particular order as I just typed them out as I remembered them.  You have to keep in mind; the severity of any of these potential mistakes will vary greatly between hobbyists based on their situation and their actions taken.   Any one of these common beginner mistakes when settin up your first marine aquarium can lead to minor problem you may not even notice all the way to completing crashing your tank and everything in between.


1. Incorrectly Topping up for Evaporation

It is very common for new hobbyist to make this mistake.  What happens is they notice the water level in their aquarium has dropped due to evaporation.  They will mix up some new salt water and add it to the aquarium to replace the tank water that was lost through evaporation.  What they don’t stop to realize is that only pure water evaporated leveling all the salt and minerasl behind.  Over time (maybe a few weeks to a month) the salinity in the tank will raise from the salt in the top up water until it reaches a high enough level to crash the tank, or the hobbyist tests the tank, notices a problem, and makes adjustments.  That is why you must top up with fresh water and not salt water.


2. Overfeeding

This can be the easiest mistake to make for people new to the hobby, and is a pretty common problem to find.  When you see your fish beg for food you might falsely assume you are not feeding enough, not realizing how much food your fish actually needs to be healthy.  Others may overfeed by feeding there fish too often each day (like 2 or 3 times a day) not realizing their particular fish will do best when fed 3 or 4 times a week. Overfeeding can lead to two different and serious problems: 1) it can have a negative effect on the long term health of your fish, and 2) you will be creating water quality problems through excessive fish wastes, or rotting fish food on your substrate, or even both situations at the same time. Both negative effects can build up in your aquarium over time and actually lead to a tank crash if not corrected.

This is an easy situation to completely avoid if you research not only the nutritional requirements for your fish but also the amount of food they should get every day or week.  These requirements and optimal feeding schedules can vary widely between the different types of marine fish so I cannot offer you a “rule of thumb” to use.


3. Starting off with a tank that is too small.

While having a small tank (ie. less than a standard 29 gallon) may seem like a good idea or an easier approach to your first marine aquarium, but it really is not. I would leave the small tanks to experienced hobbyists.  Small setups can be challenging at the best of times to maintain stability in all of the important water parameters.  Stable parameters are the key to long term success.  The larger the set-up, the more water you will have and the easier it will be to maintain your parameters.  The extra water volume will also buffer the effects of any mistakes you could make with your first setup.  And let’s face it, we have all made mistakes with our first marine aquariums.  I have read about a lot of situations were hobbyist run into serious problems setting up a 5 or 10 gallon as their first marine aquarium, struggling to keep fish, corals, or both alive in their tank for any length of time. When choosing a tank, start as big as you can afford.  If you can’t afford at least a 29 gallon tank for your first set-up, then I would suggest waiting until you can afford it.

I would recommend a standard 55 or 75 gallon tank as a very good size for your fist marine aquarium as it is a very popular larger tank size making it easier to find equipment as well as used equipment to suit tight budgets


4. Improper Salinity Levels

I am still amazed at how many people in the hobby today (new and otherwise) still under estimate the potential benefits of maintaining their salinity at or near 1.026, which is the specific gravity of the ocean at the average temperature and depth were we find most of the corals and fish that we keep in the hobby.  The lower your salinity is from 1.026, the more you will risk having challenges maintaining other aspects of water parameters.  I always prefer my salinity to be between 1.025 and 1.026. This is about 35.5 PPT (parts per thousand) for those of you who prefer using that scale/method to measure salinity.  The below link can help to explain this and other aspects of marine aquarium water parameters in a lot more detail then I am offering here, if you would like more information:

5. Not Enough Waterchanges

I have found it to be a somewhat common perception many new hobbyist to marine aquarium that you really should not be changing water.  I have often asked people with this perception what they base that opinion on.  In a large number of the replies that I have received, the person had read articles about how others will set up a beautiful marine aquarium and maintain it with next to no waterchanges.  The part that most people to not properly understand is that these are mature set-ups being maintained by people with decades of experience who have spent years researching and perfecting their skills to develop and maintain the proper balance and other requirements to achieve this. Without this background and speciality or required  equipment in place, you will need to do about 10% weekly water changes to not only replace the trace elements in the water that are required by all life forms in our aquariums, but this will also help to prevent the buildup of dissolved solids, toxins, and excess nutrients in your aquarium.  If you were to stop doing waterchanges for a month or so, you would most likely start to see degradation in water conditions likely leading to a tank crash in about a year.   The below link can help explain this a little better if you would be interested in some additional information.


6. Adding Live Rock to a Already Cycled and Stocked Aquarium

I have been asked and this question a few times worded in a few different ways, “ I have a ammonia spike and I do not understand why as I just added some more live rock to my tank, how can there be ammonia if I increased my filtration capacity?”.    I have found that many stores sell live rock and tell hobbyist that it is cured rock as the stores typically buy it as uncured live rock freshly harvested from the ocean and let the rock cycle/cure before selling it to their customers.  New people to the hobby get the impression that if it is already cured/cycled, so they can just put it directly in their already set-up and cycled aquarium without worry.  That is a false belief.  When rock (either cured or uncured) is removed from the water and exposed to the air, you will start to get die-off of bacteria and other living organisms that are on the rock.  The longer the rock is out of the water and exposed to the air, the more die-off there will be.  The quality of the live rock may also play a factor here as well. And as you know, this die off (decomposing marine life and bacteria) will add ammonia to your aquarium.  It’s not a matter of “if” but a matter of “how much”.  Sometimes the ammonia spike can be so small and so short that there is no noticeable impact to your water quality.  Other times the resulting ammonia spike can crash your tank.  You should always re-cure any live rock you buy before adding it to your tank just to be safe. The below link can offer you more information on curing live rock:


7. Not Properly Planning Your First set-up

Sometimes people will buy a used set-up or use a aquarium and equipment they had in storage setting it up as a marine aquarium then try to figure out how to make it work and what to stock in it.  This approach can often lead to disappointment or additional expense when you have to up-grade equipment.  I would suggest taking the following approach:  first decide what type of marine aquarium that you want, and then decide what you will stock in it, then start planning your set-up and all the equipment that you will need around the requirements of what you will be stocking .  The below links can help you plan your set-up:


8. Poor Quality Water and/or Salt

As mentioned above, water quality is among the most important of aspects to keeping a healthy marine aquarium.  Besides proper maintenance, another important factor of your water quality is the quality of the fresh water and the quality of the salt that you use to make up new saltwater.  Your gaol should not be to find the cheapest possible salt to try a save a few dollars.  Take your time and do a little research to find a good quality salt.  You don’t need to buy the most expensive salt out there but you do need a good quality salt. This will go a long way to help you stabilize your water parameters.  Just as important is the quality of fresh water you use, the two go hand in hand. Using tap water and dechlorinators can cause problems depending on the quality of your tap water.  This equally applies to fully treated tap water from the local water department or well water from a private well.   Just because it will work great for a freshwater setup, doesn’t always mean you will get the same results in a marine setup. Many hobbyists had learned that lesson the hard way after losing some fish and corals. The below link offers a little more information on the topic for you to consider as well:


9. Inadequate Water Flow and Movement

The ocean’s reefs where the fish and corals come from that we keep in the hobby have underwater currents and/or waves moving seawater through and around them. In order to help us have a healthy set-up, we must reproduce at least some of this water movement in our aquariums.  Without proper water flow in the aquarium, you can develop problems like: low levels of dissolved oxygen in the water, the buildup of slime,  other types of nuisance algae,  negative effects on the water quality, and prevention of some animals receiving food  just to name a few.  The below link helps to explain what proper water movement can be for your aquarium:


10. Stocking too fast

Sometimes people will get caught up with the excitement of setting up their first marine aquarium and add almost all of their planned stock in a very short period of time or even all at the same time.  The problem with adding all of your stock at once or within a short period of time to most newly set-up  aquariums is that the biological filtration most likely will not be handle all of the stock being added at once without allowing time to aquarium’s filtration to adjust and be able to handle the increase in waste being produced by the fish.  This type of situation will affect your water quality even to the point of crashing a tank in extreme situations.   The best way to avoid this is to make sure you have properly planned your filtration and you add your fish slowly over weeks or months allowing the filtration system expand to meet the growing demand.  The below link can help you better understand common approaches to marine aquarium filtration if you would like some additional information:


It may also be helpful to understand how to properly cycle a marine aquarium which will help you better understand when to start adding fish.  The below link can help with that:


11. Incompatible or Inappropriate Stock

When you hear statements like:  I can’t understand why my tangs just won’t get along, why does my trigger harass my lionfish, or my firefish went missing after I added my large lionfish, then you know compatibility was not considered when adding fish to the tank.  Also when you see pictures of 4 or 5 very small pre-juvenile tangs in a 29 gallon tank, or a beautiful snowflake ell in a 30 gallon tank, you know no consideration was given to caring for these fish for the duration of their lives.  Careful consideration must be given to ensure the fish you put in your tank can happily live out their lives together and that you know how to properly care for them.  After all, they are just not fish, but living animals.  You cannot trust the employees at a local fish store to do this research for you as the vast majority of them do not know your setup as well as you do, or they may only be interested in making a sale.  This is another reason why impulse buys often lead to problems later on.


12 Not Quarantining New Fish

One of the toughest lessons that I had to learn the hard way is the importance of quarantining new fish before adding them to your set-up.  When I was starting out in this hobby I did not use a quarantine tank and I was lucky for a quite a few years.  But then my luck ran out and I had a whole tank wiped out by adding one little fish that was carrying a disease but did not show any symptoms early on.   That was when I started learning how to quarantine fish and actuating following a quarantine process. Based on what I have read, having a tank’s complete stocking wiped out by a disease introduced from a new fish has driven more people out of the hobby than anything else.  The good news is this is completely avoidable when you follow a good quarantine process. The below link explains how to quarantine new fish as well as explaining the benefits of using one in a lot more detail should you want more information:



If you have found this article interesting you may also enjoy the below one as well

18 thoughts on “Common Beginner Mistakes with Marine Aquariums”

  1. Laurie Coleman


    this article has to be one of the best all round articles I have read, having been a keen fish keeper for quite a few years, and having kept ponds, freshwater and tropical aquariums and recently graduating to a marine reef setup, I am constantly on the lookout for information that I can study to increase my knowledge of fish keeping, and one thing I have been taught along the way is that we are water keepers, (we have to condition water so that certain parameters are kept within certain boundaries, to benefit and sustain the health of the inhabitants of the tank), in other words look after the water and the fish and corals will look after themselves.


  2. Josh

    Great info here. I have been keeping fish and propagating corals for years and I saw a lot of the mistakes I have made on this list.

    In order to conserve the natural world, anyone interested in starting an aquarium (especially saltwater) should read this. Many of us do not realize the amount of livestock that are not captive bred, but rather come from the wild. Simple facts like you listed educates the public and furthers the success of the hobby. It’s definitely not good when someone purchases a tank and immediately begins to experience difficulties. Many become frustrated immediately and abandon the tank- thus forcing craigslist to become LFS largest competitor- many of which are owned as small family businesses.

    Thanks for the article and keep them coming!


  3. Michael

    This list of common beginner mistakes is spot on, in fact over 90% of saltwater aquarium beginners make these mistakes and more and then about half of those people give up on it all together! A Saltwater Aquarium Beginners Guide coupled with the list on this page are invaluable information when looking at setting up and maintaining a saltwater aquarium for your first time, it doesn’t have to be stressful and make you pull your hair out it should be a fun and majestic hobby!


  4. Kim

    Hi! We are new, sort of, a year into our saltwater aquarium and we had been having issues with green hair algae, so finally we scrubbed all the live rock and now our tank looks worse, now we think it’s crashing. We have 5 fish, a star fish, an anemone, and lots of crabs and snails! What can we do to save them, and fix our tank problem.

    Thanks so much!


    1. Cliff Post author

      Right now, I would suggest daily water changes of around 20 to 45%. As you scrubbed your live rock, you most likely reduced the amount of beneficial bacteria that was in your set-up.

      Before you cleaned your rock, what was the salinity, nitrate, phosphate, alkalinity and magnesium levels? Also, how did you cycle your tank ? Knowing this can help me give you better advice to avoid more algae in the future


  5. Terry

    Hi I’m trying to start a salt water aquarium but I’m new to the hobby. I was thinking of a biocube 14gal. With no hood so I can purchase my own clamp led lights needed. Any suggestions on what I need to buy to start off like a list and maybe recomend brands also.thank you. Another thing I know u recommended a 29 gal atleast, but would i be able to in a 14gal?


  6. Debbie

    Hi I had a small nano marine tank that cycled for about 6 weeks i added fish and corals. I bought a new tank and want to use the live rock from my smaller tank in my new tank. Do I need to cycle my tank again for 6 weeks?


    1. Cliff Post author

      Not in all situations. You have to move enough fully seeded rock from your old tank into the new one to support all the stock going in there. You also have to be careful not to remove too much rock from the old tank. Might be best to just cycle the new tank and leave the old one as is if you are unsure


  7. Angela Milhouse

    I have a 55g to K with 1tang,1mandarin,1clown fish 2bubble tip anemones, 1elephant ear coral 1hammer coral , I restarted this tank the rock which was live is same rock but dead rock now made mistake of keeping the same sand a d I noticed these black areas in my sand bed and I’ve seed my tank with live rock that was covered with Coraline algae but I no Coraline algae could it because of the sand bed or my rocks being dead rocks I don’t know what else to do


  8. Tim

    Very good read, I couldn’t keep from laughing, thinking back to when I opened my 1st saltwater tank, a 150 gallon, I was fortunate to have a large tank but I think I made every other mistake that was mentioned….. I Would have liked to read this upon opening it, which was way back in 95, Internet wasn’t big at all yet so my info was slow……


  9. Kobus

    Hi there. I am new to the hobby, and trying to make sense of it all. Can you direct me to a guide on how to react on deviations to the normal parameters? I am not sure how to react on dangerous readings. Thank you


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