Saltwater Fish Disease Symptoms and Treatment

This saltwater fish disease page provides a listing of the more common marine fish diseases, ailments and problems with symptoms and treatments. Before you use any medication on your tank be sure to properly diagnose the disease and try to figure out why your fish have the disease. Many diseases are brought on by the fish being stressed due to transport, water quality issues or being acclimated incorrectly. If you've just set up your tank, please read about new tank syndrome in the articles section.

Always use a quarantine tank or at minimum do a freshwater dip that is pH and temperature adjusted for a few minutes. If the fish shows signs of extreme distress, such as jumping or becoming inverted, remove them from the dip immediately.

Whenever you use any type of medication on your saltwater fish, first remove any activated carbon in your filtration system. If left in, the carbon will remove the medication from the water, doing you no good. If you have invertebrates in your tank, make sure that the medication is safe to use with invertebrates (another good reason to have a quarantine tank). Read the directions on the medication bottle very carefully!

Get Some Cleaner Species

Another good idea is to include some of the "cleaning" species in your aquarium. Use caution if you plan on keeping them with Lionfish, Triggerfish or any other predatory species. There are both fish and shrimps that can perform a cleaning function in the saltwater aquarium. Some are better than others when it comes to the task of removing external parasites and dead tissue.

Some of the better ones that you'll hear about a lot are the Skunk Cleaner Shrimp and the Neon Goby. The skunk cleaner shrimps do a very good job. See the photos on the shrimp's profile page of them cleaning a Yellow Tang. Some authors have reported that the coral banded shrimp is a cleaner shrimp. We've kept them for several years and have never witnessed them cleaning hide nor hair. Maybe they only do it when the lights are off. Another fish that cleans other fishes as a juvenile is the Longfin Bannerfish. The bannerfish doesn't seem to do as good a job (and not as often) as the cleaner shrimp or the neon goby. It's really something to see a larger fish slowly approach the cleaner shrimp and allow the shrimp to climb on board to start cleaning.

Saltwater Fish Disease

Disease / Problem

Ammonia Poisoning

Symptoms: Red or inflamed gills. Fish are gasping for air at the surface.
Treatment: Ammonia poisoning is easily preventable. Avoid adding expensive and less hardy tropical fish until the aquarium has cycled. For more information on cycling your aquarium please read about the nitrogen cycle. You can use a substance called zeolite to help absorb ammonia but the best solution is to ensure that your aquarium has cycled and that your tank is not overcrowded. If your tank has not yet completed the nitrogen cycle, you will need to perform frequent Water changes to keep the ammonia levels down.


Symptoms: Bloated fish, scales are raised
Treatment: This is not really a disease, but a symptom of a bacterial infection. There are medications available but try to increase the quality of the water by performing a 25% water change. Do this once every 3 days. If your fish's condition doesn't improve, try the medication. Your local pet store should have medication for this disease. Remove any carbon filtration before using medication because the carbon will absorb the medication.

Hole in the Head - HITH, sometimes referred to as Head and Lateral Line Erosion - HLLE

Symptoms: Small holes or indentations on the head of fish, advanced cases may show markings along the lateral line of the fish
Treatment: There are many theories out there, but no conclusive scientific evidence as to what exactly causes this disease. However, it may be attributed to poor water quality, lack of proper nutrition and/or the use of activated carbon for prolonged periods. Be sure to give your fish the best water that you can by performing frequent water changes. Give them vitamin enriched foods and change out, rinse activated carbon thoroughly to remove dust or stop using activated carbon for a period of time to see if conditions improve. You might be interested in checking out this food specifically made for this: NLS Hex Shield Fish Food

Marine Ich or Ick (Cryptocaryon)

Symptoms: Small white spots showing up mainly on the fins or in advanced cases it may look like your fish has salt all over it. The fish may seem to "flash" or rub against objects in the tank.
Treatment: This is a fairly common fish disease and your local pet store or online store should have medication you can use. Ich usually arises due to stress. Many believe that you can increase the temperature of your water to 82 degrees Fahrenheit to speed up the cycle time of this parasite. Remove any carbon filtration before using medication (rid-ich) because the carbon will absorb the medication. Try to prevent this from happening by quarantining your fish in a separate tank before introducing them into your main tank. Saltwater ich is treatable if caught in the early stages. Move the fish to quarantine and medicate according to the directions on the bottle.

Nitrite/Nitrate Poisoning

Symptoms: Tropical fish are lethargic or resting just below the water surface and you are getting high readings on your nitrite/nitrate test kits.
Treatment: Nitrite / Nitrate poisoning is not a disease but will kill your tropical fish. It results from having a large bio-load on the filtration system or from not performing enough water changes. Perform a partial water change immediately and monitor the nitrite and nitrate levels closely until the situation is resolved. You may have too many fish in the tank and will need to perform more frequent water changes.

Oxygen Starvation

Symptoms: Most or all of the fish are usually found at the water surface. They may be gulping at the surface with their mouths.
Treatment: Check the temperature of the water. Higher water temperatures require higher levels of oxygen. You will need to increase the aeration in the tank with air stones or increase the flow rate with your filters. Try to decrease the temperature of the water by floating ice cubes in plastic baggies and turning off the tank light. If sun light is entering the tank from a nearby window, try closing the shades. Also, if you have an overcrowded aquarium you will definitely need to increase the aeration in your tank.

Velvet (Oodinium)

Symptoms: Velvet looks similar to ich but velvet shows up as smaller white or gray dusty spots on the fish. Tropical fish with velvet will have rapid gill movement and may be rubbing on surfaces in the tank.
Treatment: There are a lot of products out there to treat this disease. For example, Aquarisol works on ich and velvet.

Black Ich

Symptoms: Saltwater Tangs showing small black spots on their sides.
Treatment: Get a cleaner shrimp and keep your water parameters in line. Ammonia or nitrites high? Shame on you. Your tank isn't cycled and you have a whole mess of issues ahead. Wait until the tank has cycled before adding fish. High nitrates? Vacuum the sand and clean out the filters, empty protein skimmer more frequently. Also give those tangs more seaweed in their diet.

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Items you should have on hand in fish tank emergencies!