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COlumnaris? Best method to treat?


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G'day all,

I seem to be having a unlucky streak these past few days. Today I noticed one of my neon tetras in my 15 gallon planted tank was hanging out by himself and on a closer look I saw it has a small white growth on its mouth, kind of making it look like it has a flat nose. A quick google suggests its likely to be cottonmouth or columnaris. Having heard all the horror stories about columnaris decimating tanks, I immediately moved this neon to my CPD tank's empty hang-on breeder box (I stopped the air pump to cut it off from the main tank). I didn't think to acclimate the neon to its qt home, so I hope it will be ok.

Anyways how do I go about treating this neon as well as the entire 15 gallon tank? Here is the stocking:

1 Betta
2 Panda Cory
9 Neons
~20 cherry shrimp.

Last week I lost a Panda cory out of the blue, now I'm thinking perhaps it is something to do with this potential columnaris?

Water parameters:
Am - 0
N02 - 0
N02 - <5
Ph - 7.8
KH - 4/5
GH - 8/9
TDS - 208
Temp - 26

I do 30% water change once a week. These parameters were measured just before a scheduled water change, so things like TDS would usually be lower (I try to keep it around 140).

I can't seem to spot any other symptoms on any of the other fish. My main priority is to protect my betta!

This is my first time dealing with something like this. Any tips on medication and treatments would be appreciated!
I'll attach a picture of the neon just to confirm that it is in fact cottonmouth/columnaris.



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Sorry to hear one of your neons is sick and you lost a Cory! Great clear photos! Your fish has great colour!

I have had this with an odd neon maybe twice in five years, and confession time, I just euthenise the sick fish and hope it hasn't spread (and it didn't on  both those occasions). I can't get out to do anything about it anyway, so unless it has spread I wouldn't spend a lot of time and money (vet/antibiotics usually, but I don't know what is available in Australia) on a £1 fish (sorry if that upsets anyone)? I have some neons (bought this last sunday) which are a replacement for the 6 (all) that died when we had a hot week in our summer and the water got to approx. 30 degrees on a few days and killed them all off - incidentally the Ember tetras survived in the same tank with out a problem. I think neons are pretty fragile/weak. If you can, I would try and keep the temperature at 24 but that may not be possible where you live?

I believe the bacteria that causes it is always present in tanks and only causes the lesions when a fish is stressed or weakened, usually poor water quality is the preferred culprit! Unlikely in your case though!

If your water is going from TDS 140 to TDS 200+ between maintenance/water change, do you know what is causing that? Do you get a lot of evaporation? I would think the weekly water change of 30% should be sufficient, though try and add the new water slowly.

The water parameters you have are obviously as a well researched BALANCE/Compromise for the variety of fish/shrimp you have and I wouldn't think they would be a problem! Neons prefer a lower PH and softer water in general I believe. How long have you had this setup running?

You may have already seen the below but I think it is a good overall article,



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Thanks Simon,

That's fair point for $1 fish haha, I guess I was also worried about the rest of the tank, but since I can't seem to see any symptoms or oddities on the other fish I'm hoping its all good and all I can do is keep monitoring and just see how this qt'd neon goes.

Yes I am getting alot of evaporation now that it is summer. Temp goes up to 26 max so far during the day and drops down to 23/24 at night. 

Adding water too fast is maybe something I'm guilty of, I use a bucket and just pour it in. 

Yeah the PH isn't ideal, maybe it is indeed something to do with my RO water and remineralising. This tank has been running for almost 4 months now. It has driftwood and Amazonia soil, so maybe why it is able to pull the PH down a bit more effectively than my other tank with 8.2/4 ph. I also use "Black Cole Stone" in this tank, which I have no idea what exactly it is and cant seem to find anything about it on the net, so I dont know how it affects ph

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Hopefully by removing the sick fish the others may be alright, as mine were. You are doing the right thing and keeping an eye on the remaining fish!

I am quite surprised to hear that you are using RO water and remineraliser! If you top up the tank between water changes you should top up with pure RO water, otherwise you will get a build up on the parameters, as evaporated water leaves all the minerals in the tank.

Even if you just get a small diameter piece of tubing and let the water syphon in from the bucket will be less disruptive and more gradual?

The rock may be affecting the PH, try tesing the PH of the new prepared water before it goes into the tank. If the soil is reducing the PH and fighting the rock then the Ph will rise a lot more when the soil is exhausted, and the soil may get exhausted quite quickly.


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  • 4 weeks later...

Hey! Ah sorry, yes I only use remineraliser when I do waterchanges not top ups!
All other fish seem fine since qting that particular neon. The neon is still alive (almost a month now since qt) which makes me think it may not be columnaris as I've read that it is fast acting. Its been behaving normally this whole time but the white growth on its nose is still there.
This is the treatment I've been conducting since I already had these on hand:
I've been using both Melafix and tBroad Spectrum Remedy in minimal amounts as the qt tank is a small breeder box of ~700ml. I used 0.5ml Melafix and 3 drops of BSR.

At one point it seemed like the white growth was decreasing in size. It reduced revealing pink/red underneath on its nose. However a couple days later the white growth had regrown. So from what I can tell it seems to be like a cycle. The white growth eventually kind of peels/flakes off revealing the pink/red (wound?) underneath before the white growth reappears. The neon is still alive and behaving normally. Any tips? 

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Good to get an update!

I would carry on as is with the neon seperate until you are really sure it is ok and not risk putting it with the other fish.

I got some new neons before xmas and one seemed to have this but I haven't seen it recently so it either recovered, or died (can't remember how many I bought???). My (albeit limited) experience with neons is they aren't very robus/strongt, but are easy to get, pretty, and very cheap. Taking that into account I would tend to dispose of any sick ones I find, though I only do this with neon tetras.


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Good read! I'm noticing one of my angelfish. I guess I could take Simon's advice on how to take care mine. Good thing I found your thread here guys. Thanks! 🙂

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