Little in this hobby stirs up as much emotional debate as discussions on quarantining fish. Threads on prophylactic treatment, ich management, and immunity are regularly hashed out until people are burned out. Passions run high, and for good reason. Both sides of the debate feel their practices are what are best for the fish, and they all care deeply about the health of their fish.

The display tank of @Brew12.

Photo is courtesy of the author, @Brew12, ©2019, All Rights Reserved.

I will admit it. I am a hypocrite when it comes to this topic. Every fish in my tank has been treated with copper or chloroquine phosphate. Most have also been treated with Metroplex, Kanaplex and praziquantel. Almost every fish I have received has had Cryptocaryon irritans, Amyloodinium ocellatum, flukes and/or uronema. I feel that my greatest chance of successfully keeping healthy fish is through treating for these even if they aren’t showing symptoms. And yet, I know that this is not sustainable. The future of this hobby will depend on us getting away from prophylactic treatment. I know this, and yet I can’t get myself to change. I am certainly a hypocrite.

The freshwater world of cichlid-keeping experienced a crisis due to overuse of prophylactic treatment. African cichlids routinely developed bloat. It was found that bloat could be easily treated using metronidazole. With everyone using metronidazole, keeping cichlids became easy. Many fish were saved that otherwise would have been lost to bloat, and the cichlid hobby lived happily ever after.

Except that isn’t how the story went. It took less than 10 years before metronidazole become completely ineffective against cichlid bloat. Fish deaths increased, and the only known cure was no longer effective. Fortunately, it was found that a natural food could be used that would prevent cichlid bloat. This cheap and readily available “cure” was widely adopted and keeping cichlids was easy again. Interestingly enough, several years after it fell out of widespread use, metronidazole became effective again and can still be used to treat acute cases of cichlid bloat.

An African cichlid, Cyphotilapia frontosa.
frontosa-1323598_1920 (3).jpg

This is a royalty-free photo courtesy of Christy Hammer from Pixabay.
What are we going to do in this hobby when copper no longer kills ich (Cryptocaryon irritans) or velvet (Amyloodinium ocellatum) at levels that aren’t also fatal to the fish? How will we react when praziquantel-resistant flukes become the norm or when internal parasites and bacterial infections no longer respond to metronidazole or kanamycin? I believe this is inevitable, and the more widely used these products are the sooner it will happen. I feel we need to start planning for this sooner rather than later.

Typical meds.

Photo is courtesy of @Brew12, ©2019, All Rights Reserved.

Fortunately, we do have people who have successfully kept fish without prophylactic treatment that we may be able to learn from. I’ve tried to gather as much information as I could from them and figure out what they have in common; I wanted to share my observations.

Fish Nutrition:

The immune system of a fish is a fascinating thing. This immune system is fueled by the food the fish consumes. It is more than having the right amount of proteins, fats, vitamins and minerals although those are also important. Gut microbiota (probiotics) play a critical role in the health of a fish. The most reliable way of supplying microbiota is through fresh live foods. That isn’t an option for many of us but frozen foods can be almost as good. All frozen foods made from quality ingredients will contain some of the necessary bacteria. Some frozen food suppliers, such as LRS Foods, add probiotics to their foods prior to freezing. It is important to minimize the number of times the food is thawed and re-frozen as each cycle will kill additional bacteria. There is nothing wrong with using pellets or flake food but they should be supplemented by at least some fresh or frozen foods on a regular basis.


Photo is courtesy of LRS Foods. ©2019, All Rights Reserved.
Feeding the proper amount is also important. Feed the fish what the fish need to be healthy. If you are cutting back on how much you feed because of algae issues or to try and reduce nitrates you are risking the health of those fish. Find other methods to address those issues. Properly fed does not mean overfed. One feeding a day should be plenty for most fish. A healthy tank will have pods and algae that fish will graze on to supplement what you provide.

Fish Stocking:

Stress is the enemy of the fish immune system. One way we can reduce the stress on fish is to make sure we are stocking our tanks properly. Thanks to the Tang Police, we know we should take the fish size and swimming habits into consideration when determining if a fish is right for whatever size tank we have. We do need to take compatibility into consideration when it comes to stocking our tanks, too.

We need to take aggression level into account. We may not be able to keep two similar fish or two of the same species together. Some wrasses can be mixed easily but other combinations may not work. Do your homework prior to going to the fish store. Keep in mind that we aren’t looking for fish that might be able to get along if we are lucky. We want compatible fish that will live together with minimal stress.

Another thing to keep in mind is that we may need dithering fish to keep stress down. Some fish may hide unless they see other fish swimming around for fear of a predator being nearby. Dithering fish are fish that will more readily swim in the open to reassure the less assertive fish that the area is safe. This has the side benefit of drawing your shy fish out for more public observation.


We should expect any fish we purchase to be in a stressed and weakened condition. They may have been plucked from the ocean and moved through several systems along with multiple overnight flights over the course of a week. Odds are they have not been fed well during this time, if at all. Unless your system doesn’t have other fish yet, or is extremely peaceful, it may be best to not just dump the fish into your display to fend for itself. At the very least I would recommend using an acclimation box for a few days. This will allow the fish time to adjust to your system and feeding regime without having to compete with its tank mates. Another option, if your system has room for it, is to let the fish acclimate in the sump for a few weeks and then move them into the display tank.

It is also not unusual for local fish stores and wholesale suppliers to keep their fish in water with a salinity below 1.017. Some fish can adapt to a sudden increase in salinity to 1.025 but others may struggle. For this reason alone it may be worth setting up a quarantine system to keep the fish isolated while gradually raising salinity over the course of a week. The fish can also adjust to your feeding habits during this time giving you a better chance for success when you do add them to the display tank.


There is more to aquascaping than just making it look nice. We want it to meet the needs of our fish. Are we going to have enough hiding spots for our fish? Do some fish need a sand bed? Will the fish have enough open swimming area? Will they still have enough swimming area when the coral grows in? One sure way to have aggression is to not have a place for each fish to hide at night and aggression leads to sick fish.

System Stability:

This is a very broad term and I am only going to hit the highlights. We should do our best to provide a consistent environment for our fish. We should monitor our systems regularly to ensure all our equipment is operating properly. It is important to keep spare pumps and heaters so we aren’t panicked if we have a failure on a Saturday night. A heater controller is also a great idea as temperature spikes have been known to cause disease outbreaks in tanks. Using an ATO system will help if we can’t regularly top off the tanks manually.

Parasite Control:

If we have weakened fish that we have just added to our system, it will help to have a system in place to help limit the number of parasites that can attack the fish. The most commonly recognized methods of parasite control are ultraviolet (UV) filters and ozone. Most UV filters have two recommended flow rates, one for algae and a slower flow rate for parasites. Ozone generators can be used to damage the cell walls of the parasites and kill them before they infect the fish.


Photo courtesy of @Brew12, ©2019, All Rights Reserved.

Another observation I have made is that people who are successful keeping fish without prophylactic treatment are well populated with corals having large polyps. We know ich and velvet need hard surfaces to attach on so that they may reproduce. Fewer hard surfaces due to coral growth may make the parasites travel further prior to finding a place to attach. Coral polyps are known to eat copepods and other small organisms. I suspect that they also eat the parasites both looking for a place to encyst and again as they get blown around trying to find a host. If I ever do set up a system that doesn’t rely on prophylactic treatment I will load up on these natural mouths by adding Green Star Polyps, Zoanthids, and any other corals that can directly consume small organisms.

Another way parasite control happens in a more mature tank is through "decoy" fish. The free-swimming parasites have no way of knowing which fish in the tank have a strong immune system and which have a weakened one. Parasites that land on a fish with a strong immune system will reproduce in very low numbers, if at all, which will help protect newly added weakened fish while they build their immunity.

The display tank of @Lasse.

This photo is courtesy of and used with permission from @Lasse, ©2019, All Rights Reserved.

And quickly, I want to address something that doesn't work. Cleaner fish and shrimp are not likely to have much impact on the parasites and only clean up the mucus and dead skin from the parasite entry location. There is no evidence that either will eat the parasite itself.

I hope people out there who are struggling with fish disease but don’t want to treat prophylactically have found this useful. And don’t feel like you need to do each of these perfectly, just do as well as you are able. The better you do any of them, the more likely you can have a failure in a different area while keeping your fish healthy. A poorly fed system that is overstocked with aggressive fish will do much worse during a heater failure than a system that is well fed and properly stocked.


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Author Profile: @Brew 12

Steven Frick has spent much more time under the ocean than keeping a small piece of it. He got his start in the electrical field in the US Navy Nuclear Power program as an electrician's mate. After 5 years of service on the submarine USS Henry M Jackson he finished his final 3+ years of service teaching electrical theory at the Knolls Atomic Power Laboratory.

Currently, he runs the projects and maintenance for the power distribution system of one of largest electrical consuming heavy industrial companies in the Southeastern United States. He wrote his sites' electrical safety policies and routinely acts as a consultant to other industrial facilities looking to improve their electrical safety programs. As someone who loves to both learn and teach, he has focused his attention on his newest hobby, reefing.