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Sunday, April 8th 2018, 1:16pm

Sick Corydoras sterbai - fungus - help!


Please excuse this English-language post. Although my grandfather came from Austria and my family is in fact named after the giant Wels catfish of the Danube River, we have lived in South Africa since the 1930s and the German language has been lost.

I have a quite new 40-litre planted tank with 1x Betta splendens, 7x Neon Tetra and 4x Corydoras sterbai. The tank is kept at 25 degrees C. The fish are fed commercial crumb-type food. I used to keep many aquariums in the late 1980s. This is the first fish tank I have set up since then.

The fish were all obtained about a month ago. The tank has been up and running for about 6 weeks. In the last two weeks I noticed one of the C. sterbai (Cory #1) had a very small patch of fungus (1mm across) on its forehead between its eyes. This fungus has not become bigger in this time.

In the last two days I noticed another of the C. sterbai (Croy #2) has a larger patch of semi-transparent fungus in front of its dorsal fin. The dorsal fin of Cory #2 is also not whole; it has never been whole since I got the fish, but it might be rotting back, I am not sure.

All the fish in the tank are behaving as if they are very healthy. The Neon Tetras even showed spawning behaviour two days ago.

I have uploaded photos of Cory #1 and Cory #2 to this link:…h4Z2uOejha?dl=0

If anyone could help with a diagnosis and advice on how to treat this fungus with the minimum of disturbance to the other fish in the tank, I would be most grateful!

Thank you very much!

Adam Welz
Cape Town, South Africa

Joern Carstens


Posts: 401

Location: im hohen Norden

Occupation: Wasser-Panscher

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Sunday, April 8th 2018, 5:16pm

Welcome, Adam.

Looking at your Corys it seems to me, they are quite o.k. - desite the patches you mentioned. Something like fungus, i agree.

Question: Water change - how often do you do this ? In your relatively small tank I would recommend something like a weekly change of 50% - just to minimize all germ / mircobes and fungus in the water.

I recommend some industrial medicals (i don't know what you can get in South Afrika) something like JBL Fungol or something equivalent from other companies. Yes, you treat the whole tank - just to minimize infection of other fish.

After or parallel tro that therapie additional you may add something like see almond leaves. Here, "at home", we use "Erlen-Zapfen", the fruits from Alder trees that conatin (as sea almond) much tannic acids and other ingredience that reduce bakteria activity. Also dried wallnut leaves.
Probably you con get something like that in S.A. ?

All the best to your fish !
Beste Grüße


Monday, April 9th 2018, 9:52am

Hi Jörn,

Thanks so much for your reply!

I got my tank water tested yesterday just for 3 basic parameters.

pH was 7.6
Nitrate (NO3) was about 12mg/l
Ammonia 0.1mg/l

The local aquarium store owner thought that nitrate was too high, and I was having some "new tank syndrome". He suggested 25% water changes every second day for a week and not feeding the fish for a week. With every water change I should add Seachem Prime and Stability (which I have). He thought that anti-fungal medicine would not be needed.

I'm not sure if not feeding the fish for a whole week is a good idea. What do you think?

Thank you in advance for any reply!


Adam Welz

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Used tags

Corydoras, fungus, Sterbai