9 Tips to Maintain a Healthy Marine Fish Aquarium

Blueface Angelfish (Pomacanthus xanthometopon) in a display tank with other specimens

Blueface Angelfish (Pomacanthus xanthometopon) in a display tank with other specimens

There’s no better teacher than experience, and with nearly a half century of saltwater aquarium keeping under his belt, Richard “Dick” Hilgers certainly has plenty of experiences to share! Currently the owner of The Cultured Reef, a coral-aquaculture facility located in Fort Pierce, Florida, Dick first took the plunge into the saltwater hobby back in 1966. Since that time, he’s had his share of successes and failures and seen a lot of trends come and go. Along the way, he has also identified many fundamental principles that lead to success in this wonderful hobby, which he has graciously agreed to share with us here at Saltwater Smarts. We’re thrilled to welcome this “seasoned salty” to our family of contributors! (Editor)

One of the challenges hobbyists face is keeping their saltwater fish (and corals) in a good state of health. I have personal experience with failure in this area. In 1966, when I set up my first saltwater tank, I was so excited. The beautiful vibrant colors were breathtaking compared to the freshwater fish I was keeping. After 20 years in the freshwater hobby, it was time for me to make the leap to saltwater fish. That was all we could hope to keep alive at the time.

Inauspicious start
I set up a 29-gallon tank with an Eheim canister filter and heater. That was back in the marine tank “dark ages.” I did know enough to cycle the tank because of my extensive freshwater experience. I don’t remember what my first fish was. What sticks in my memory bank is the wipeout I experienced in the first 30 days. Everything was dead! I made what today would be considered classic mistakes.

There was precious little literature on saltwater tanks back then. When the first book came off the press covering the keeping of saltwater fish, I devoured it. The author, Robert P. L. Straughn, wrote The Saltwater Aquarium in the Home in the late sixties. The book was to change my luck with keeping saltwater aquariums. I was so impressed with the author that I made the effort to travel to Florida specifically to meet Mr. Straughn in person. He proved to be the most knowledgeable person in keeping saltwater aquariums at the time. Bob was also very generous with his time. I learned a life-changing lesson from him—to share your knowledge freely with others.

Lessons learned

Now, 47 years later, it is my intention to help you avoid some of the pitfalls of maintaining an aquarium of healthy fish, corals, and invertebrates. For the most part, it’s the fish that give the newbie and ill-informed the most trouble, so I’ll concentrate on them, but the information applies as well to all marine animals you’re likely to keep in your aquarium.

The most logical place to buy marine fish is in a pet store, commonly referred to here as your local fish store (LFS). The LFS is also the most likely place you will seek advice. The advice you get will direct you to success or failure depending on the purveyors of said advice.

I cannot stress enough that it is your responsibility to gain the education you need to succeed in this hobby. If you are to be successful at maintaining a marine aquarium, you must learn the basics and then expand on that knowledge through research. Here are some basic lessons in fish buying and keeping that I learned, practice, and pass on to all who will listen.

1. Don’t get caught up in the beauty of saltwater fish

This fascination can lead to a false belief that the fish is healthy. You must learn to look beyond the beautiful colors. You should be looking for the markers of disease, for example:

  • Rapid gill movement
  • Erratic swimming behavior
  • Sulking in a corner or at the top of the tank
  • White spots on the body (potentially ich)
  • Fins that are frayed or torn
  • White fuzzy patches (fungus) on the body or fins
  • White clumps of cauliflower-like growths on the fins (Lymphocystis virus)

Look for anything unusual that shouldn’t be there. If you see anything at all, it’s best to pass on that fish and probably wise to avoid any fish in the same tank.

If that tank is on a central filtering system, it’s probably best to not buy any fish at this time from that LFS. Some LFSs routinely dose their system with a copper-based medication as a prophylactic treatment. You need to know this before making a purchase, as copper is extremely toxic to corals and invertebrates already in your system. Don’t be afraid to ask questions of the LFS employee.

The goal is to buy fish that have a reasonable chance of being healthy at the start. If it doesn’t look healthy and perky and isn’t looking for food and swimming normally, don’t buy it! Avoid it like the plague because it may have the plague and generously pass it around, causing you much grief and money.

2. Always ask to see the fish eat

Fish are captured on faraway reefs days and even weeks before they arrive at your LFS. They are not fed during this period to allow them to empty their intestinal tract. The reason is to avoid them dumping their waste in the transit bag and contaminating the water with ammonia. Ammonia is highly toxic and kills quickly, so starving them for a few days is a good thing. However, it also adds to the stress of being bagged multiple times, transported, bounced around, and subjected to several changes of water before finally arriving at your LFS.

Fish come in hungry and stressed, and problems occur regularly. They often refuse to eat even though their gut is empty. Ask the LFS employee to feed the fish in front of you. Most will gladly comply with your wishes. If they won’t, seriously consider looking elsewhere. You want a fish that is already eating. It’s tough to start a car that is out of gas. Likewise, it’s tough to get a fish to eat if it is refusing food at the LFS. Don’t be afraid to ask, and don’t hesitate to pass on that fish. There will be many others to choose from.

3. Trust your gut feeling

If all looks good but you’re hesitant about the purchase for whatever reason, ask the LFS to hold the fish for 24 hours. Be sure to go back in that time frame and check the fish again. Ask them to feed it again. It helps if you are a regular customer. Be sure they mark the tank with your initials to indicate that the fish is on hold.

4. Don’t buy on impulse

If you tend to buy on impulse, put the fish on hold for 24 hours. Give your tank at home a thorough check to see if the critter will actually fit into the current scheme of things. Oftentimes you will avoid disaster by changing your mind. Be sure to go back to inform your LFS that you’ve changed your mind. At this point a simple phone call will suffice.

5. Research first

Usually, it’s after several hard-learned lessons that we begin to see the importance of researching a potential new fish purchase. Be different; know that research is one of the keys to success in marine aquarium keeping. Another reason to put a fish on hold is that it gives you time to do the research before you actually make the purchase.

6. Begin building a library

There are myriad books on the subject of keeping marine fish and other critters along with mega gigabytes of online information. You can’t possibly remember everything about the successful keeping of a marine tank. Build a library and use the internet; it will pay for itself in no time.

7. Don’t accept anyone’s charity

Discourage others from buying new fish or other critters for your tank (without your knowledge). Good intentions often cause serious disasters. You are and should be the only person responsible for making decisions on what is added to your system. If someone hints at bringing you something for your tank, request to go with them to make the purchase. That way, they get to honor you with the gift but you get to choose what it will be.

8. Give your fish the best food available

Today’s offerings sound like a gourmet restaurant’s menu with items like brine shrimp, mysis shrimp, krill, silversides, scallops, clams, cyclops, squid, rotifers, ocean plankton, and the various “blends” that mix things up. Let’s not forget the many flake and pellet foods. The variety seems endless. Do not pick one or two items to the exclusion of all others. Mix it up and feed a variety. Your fish will reward you with great colors and health.

9. Quarantine every purchase

Tens of thousands of marine fish and other critters have been lost due to the lack of a quarantine system. We must learn and practice good marine husbandry to lessen the demand on our delicate reef environment. We must become responsible reef keepers. One way to achieve this is to set up a simple quarantine system and to quarantine all new specimens for at least four weeks.

Using the above methodologies, I’ve had extraordinary “luck” at keeping my fish healthy for extended periods of time. My personal best is an Amphiprion percula that survived for ten years and then was given to another hobbyist when we moved to Florida. I lost track of him after that. Anyway, happy reefing!


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Great post Dick, please keep them coming.

    • Chris Aldrich says

      Thanks for taking a moment to comment, Dmac! As a veteran of the hobby, Dick is a great resource with a wealth of information. We look forward to bringing you more of his great insights. Cheers!

      • Really good advice and a nice read. One thing i will add is that all shops, books and blogs say to quarantine fish before introducing them into the main aquarium. Great advice if you have a quarantine tank, however the majority of casual fish keepers simply don’t have a spare tank complete with heaters, mature water, power heads etc. So i personally think there should be articles focused on people without quarantine tanks. Just a thought as i know many people with aquariums and only one has a quarantine tank, which is me.

        • Chris Aldrich says

          Hi Nick – We always advocate for a quarantine tank but understand there are folks who might not see the value. With deals that can be found on Craigslist, saltwater forums, and from local reefers, it’s very affordable to snag a used aquarium and even the equipment needed to put together a quarantine system. An effective QT system need not be extravagant (https://www.saltwatersmarts.com/quarantine-tank-aquarium-success-531/), but it can be a literal lifesaver for inhabitants already in the display. The slight added expense up front will be a pittance compared to the cost of battling a disease, or worse yet, having to restock an entire aquarium. That causes many folks to leave the hobby altogether.

          By the way, glad to hear you are a QTer!

        • Hi Nick, For those who do not see the need for quarantine systems, don’t want to spend the extra money for a QT, or don’t have a clue that the beautiful fish in the LFS can wreck havoc in their DT without being QT’d, I highly recommend they run a UV Sterilizer of adequate size (or larger) on their DT system.

  2. Matt Bowers (Muttley000) says

    Very nice write up here, thanks for sharing your experience! If you get a chance to comment, I would be curious as to what is the most obscure thing you have kept over the years?

    • Thank you Matt. Not sure what you mean by, “what is the most obscure thing you have kept”, as obscure means, “not discovered, unknown, uncertain, not important nor easily understood”. So I’ll go with the idea you are looking for the most rare. Even that is hard to define as my SW keeping time period spans 47 years. What was rare back then is not rare anymore. One thing came to mind as easily the most rare back then.

      In the early ‘80s, on a weekend trip to Chicago, I found 4 different LFSs displaying the Mandarin Dragonet, Synchiropus splendidus. Can you imagine my shock discovering this beautiful fish with it’s striking colors, outlandish pectoral fins, tiny mouth and slow motion but deliberate swimming style? I was hooked!!! But the prices ranged from, as I recall, $1000 down to $300 for one specimen. Well, needless to say I had to pass on them. Two weeks later in a shipment, I received my first Mandarin Fish. I was elated that it made it alive. Of course it starved to death. Little did we know then, it required live foods. Of course things have changed a lot since then. Now we know wild caught Mandarin Fish require a large population of copepods and other live foods to survive and that requires a rather large aquarium to accomplish, without constant replenishment. Great strides have been made today with captive breed and raised mandarins eating frozen food offerings. A great reason to buy tank raised SW fish of all kinds.

      Another rare event happened a couple of years ago. I found an Orange Spotted File fish, Oxymonacanthus longirostris, at a LFS that was devouring live brine shrimp. I know they prefer coral polyps as there main diet but had to take a chance on this little guy. So the owner sent me home with him and a generous amount of live brine. Well, this little cutie was put into my 135 gal mixed reef with some real aggressive eaters. A 4” Sohal Tang (Acanthurus sohal), a 4” Desjardinni Tang (Zebrasoma desjardinii), several Red Stripe Anthias (Pseudanthias fasciatus), and many other fish. In short order the Orange Spotted File fish was hogging down everything INCLUDING Nori algae off the veggie clip, competing with the Tangs for space and bites off the clip. He lived for two+ years with me. I have photos of him doing this but not sure if pics can be posted in the comment section.

      I hope this satisfies your question.

      Happy Reefing comes through research!


  3. This is indeed a great post. Thanks for sharing this to us and keep posting. This will really help homeowners.

  4. I agree that one of the challenges hobbyists face is keeping their saltwater fish (and corals) in a good state of health. Great post! Those were amazing tips and will surely help homeowners. Thanks for sharing!

  5. Thanks to all for posting. Maintaining a saltwater aquarium is relatively easy if you know and follow some simple rules. Deviating from the rules will eventually lead you to disaster. I encourage people to keep researching. This is not a read one book and your done project. This should be looked at as an ongoing lifetime study. Learn the basics and then expand your knowledge by continued research. This hobby is not static, it’s ever changing with new products and techniques appearing on a regular basis. By taking an active roll you will enjoy this most fascinating hobby for years to come. I haven’t lost my interest in learning something new for the past 46 years. I’m looking forward to many more even at 75 years of age.

  6. That’s a great position you folks have been carrying out there. Well said that there’s no better teacher than experience. One of my challenges hobbyists face is keeping their saltwater fish (and corals) in a good state of health.

    • Thank you for your comment, Sofia. Maintaining any living animal in a good state of health comes down to good husbandry. In the case of SW fish and corals, I would advise hobbyists to pay particular attention to water quality. You must begin with pure Lab quality water through the use of an RO/DI filter unit with a TDS reading of zero. Next would be a good brand of salt, of which now days there are many. If you are going to include corals in your display it becomes more important to seek a high quality salt designed for corals such as “Reef Crystals” or Tropic Marin as two suggestions, there are probably others. Next, diligent testing for water parameters and doing necessary adjusting them to keep them in a safe range through water changes, adding chemicals as needed, plus using quality absorbent filtrates such as Boyds Chemi Pure. I strongly recommend quarantining all fish for thirty days in a separate tank set up as a “spa quarantine” system. For a more thorough explanation of my recommendations on buying fish and corals plus my “Spa Quarantine” system go here – http://theculturedreef.com/nine-rules.htm.

      I hope this helps you and others, Sofia.


  7. Thanks for the tips on taking care of tropical fish. I appreciate you you mentioned looking past the pretty colors to see if the fish might have any problems. I can see how it might be distracting to have such beautiful fish! However, the fish’s health should always come first.

  8. Hi am starting a salt water tank it is my first and I went big and bought a 100 gallon tank I have done all my resher and have found your article the most informational thank you for th info

    • Thank you, Lucas,

      You are starting with a good size aquarium. Most people start with a much smaller size and almost immediately run into trouble. Larger volumes of water remain more stable over time and give the hobbyist a cushion of time before a disaster presents itself. You must be diligent with testing your water parameters, adding RO/DI water for loss due to evaporation, and saltwater changes on a regular basis.

      I enjoyed the saltwater hobby and business for 50 years and 20 years prior in freshwater. I retired July 31, 2017 as I was approaching my 80th birthday December 4th. Time to relax. Here is a link to more informative articles on my website. http://theculturedreef.com/education.html I’m not sure how long I will keep the website open so read them soon.

      Thanks for the compliment. Happy reefing.


  9. I agree that one of the challenges hobbyists face is keeping their saltwater fish (and corals) in a good state of health. Great post! Those were amazing tips and will surely help homeowners. Thanks for sharing!

    • Dick Hilgers says

      I’m happy you found value in my post. Too many hobbyists, especially beginners, are so taken by the shear beauty of SW fish and corals they very often doom themselves to failure without knowing it. Education through bad experiences is very costly. Three things I recommend doing is to research, research, and research some more.

      No person in their right mind would jump into an airplane and attempt a take off with out training. They would surely crash and burn. It’s no different with the SW hobby. Too many new hobbyists do crash and burn because they don’t take the time to do the research before starting. Unfortunately, they take a lot of SW fish and corals with them.

      Happy Reefing,


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