What's new

Help with new fish keepers and our tetras

🐠 March TOTM Starts Now! 🐠
FishForums.net Tank of the Month!
Click here to enter!


New Member
Dec 8, 2023
Reaction score
Hi, my name is Cain and me and my fiancé have started our very first tank a few months ago and have run into some issues. I have attached some pictures of our neon tetras. The problem is two of them are showing some issues, one has a white growth on its mouth and seems completely fine other than this growth. (He has no issues with schooling or eating) however the other one with the white cotton like growth is breathing rapidly and seems to avoid other fish aswell as does not eat often. We have treated the tank with both melafix and pimafix with no results. Also after treatment our blue guarami seems to be less social and stopped eating as much (however he’s coming out more now so I think it was bringing back the charcoal filtration to remove the medicine is helping him). We’ve also noticed an increased amount of brown like algae all over the tank that is easy wiped away but we aren’t sure if that’s okay or not. Now me and my fiancé are stuck and would love some help from the forum as we are both very new to the fish keeping scene.

Tank size: 20 gallon
Filter: marineland 125 with just the filter it comes with
Heater: yes
Fish: 7 neon tetras, 3 peppered Corey’s, 1 blue guarami

TLDR: a few sick neon tetras shown in the below pictures, any help would be great!


  • IMG_7380.jpeg
    220.1 KB · Views: 15
  • IMG_7378.jpeg
    153 KB · Views: 10
  • IMG_7376.jpeg
    300.9 KB · Views: 8
  • IMG_7377.jpeg
    332.6 KB · Views: 8
The neon tetra with the white lump on the bottom lip has what I consider to be a virus that is reasonably new to science and has been showing up during the last 2 years. The fish continue to swim and eat normally and should be left alone until it can't eat or swim properly, then euthanised.


The neon tetra with the white stuff on the body is suffering from an internal issue (probably intestinal worms and or gill flukes) and is covered in excess mucous. The mucous is produced by the fish when it is irritated by something in the water (ammonia, nitrite, nitrate, incorrect pH or an external parasite).

If the water quality is good (0 ammonia, 0 nitrite, less than 20ppm nitrate, pH around 6.0 to 7.5) then it is either from the medication or an external protozoan infection.

Did the white stuff on the neon show up before or after you added the Melafix & Pimafix?
I'm assuming before you treated and this would support poor water quality or an external protozoan infection.

Poor water quality can be treated by doing big (75%) water changes and gravel cleaning the substrate every day for a week (or more if required).

Some external protozoan infections can be treated with salt, (see directions below).


The blue gourami is probably stressed from the Melafix and Pimafix. These medications leave an oily film on the surface and labyrinth fishes (Bettas & gouramis) regularly take air from the surface. If there is oil on the surface the fish get that on the labyrinth organ and gills and it can kill them or cause them to have trouble breathing. Clean water (big daily water changes) and surface movement (aeration) should help.


What to do now.
Test the water for ammonia, nitrite, nitrate and pH.

Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate every day for a week. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk. If there's a water quality issue, the water changes will dilute the harmful nutrients (ammonia, nitrite & nitrate).
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

If there's no improvement in the neon tetra covered in mucous after a week, add some salt and maybe look at deworming the fish. You can use deworming medications and salt at the same time.

Section 3 of the following link has info on deworming fish.


You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water (about 2 litres) and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.
Welcome to the forum to start with... :hi:
Colin has given you some advice. And as being a novice aquarist, it would be wise to take his advice with this affected tetra.

Most reactions


Staff online