Can corydoras try to kill eachother?

Hey, I know how this sounds but hear me out for a second. For some reason I always end up with just a pair of cory, no matter how many I add or what happens.

I started my first tank 2 years ago and after cycling for 2 months I added 2 cory panda, 2 nerite and a female betta. I monitored them carefully for a few days and since the betta didn't bother them at all I added another 5 cory. 1 died in the first week (he seemed sick from the beginning) and in the following months I ended up with only a male and female. My parameters we're fine all the time and the tank has always been heavily planted.

I got 3 more cory after I checked everything possible and again, after 1 month I ended up with only 2, but not the first 2. I always tried to pay attention to the betta, but I've never seen her try to bite a cory.

After another month I got 6 albino cory, because they should be hardier, but again, after a few month I only ended up with a male and a female. Since then, i've had the same 2 albino and 2 panda for a year, with the betta and 2 snails.

I thought that because they always ended up being a male, female pair maybe they stressed eachother out until only 2 of them remained. I know, I myself don't really believe this but I don't know that to believe anymore.

A photo from back then to see how the tank was planted:
The tank is 40L
25-26⁰C with heater
HOB filter and an air stone for more surface agitation
Aquasoil toped with sand and some root tabs
8h of light about 800 lumens
Micro, macro, carbo

 

I don’t think Corydoras can per se kill each other. However established Corydoras can stress out new arrivals and the stress can potentially kill them. The betta could also be killing them (though it’s unlikely) as bettas do not like new arrivals at all. They will often attack many new fish added to their territory.

 

I don't keep Cory's, I've never been able to keep them alive for more than a week when I tried.
There's this:
The Cory Toxin | Corydoras Forum

They do have stinging spines, they can in theory injure or kill another fish in defense, and there are sponge species of cory that are worse than others.

As bottom feeders they are susceptible to bacterial infections though. You really gotta keep your eye on them and keep a clean tank to avoid them getting sick and needing treatment or dying.

Are they that hard though? For me yes, other people seem to like them and not have the problems I have with them. Any time I've tried them, they don't thrive and die in a week or so, so I gave up on keeping them.

 

Hi, in the main corys are peaceful and get along just fine, any chasing you might see is more likely spawning behaviour, some videos of spawning here https://www.fishlore.com/aquariumfishforum/threads/corydoras-spawning-videos.455564/

There are a few species such as C.semiaquilus & some other long nose corys where males can get aggressive when spawning but they’re not the species you have.

As for the toxin that also isn’t an issue in a tank, it’s more often seen when transporting corys where any toxin released in the bag in the small amount of water can kill them and it happens quickly, some species such as C.sterbai are more prone to releasing it than others.

If you have tested your water and all is good there then I’d be looking at the Betta as a possible culprit, though in more recent years C.panda seems to be quite delicate and difficult to keep.

 

How big is your tank? It looks well planted. Are there any caves set up for the corys? Corys do like to have hiding places.

 

I have Kept cories and they are quite Hardy, however they can have trouble being fed properly, especially new arrivals.Dont overfeed but they should stay bulky and fat. In my experience, don't overfeed but it is better to feed ro much and do a big water change then too little. Also cories really love flow and a LOT of oxygen in water, which is why they aren't great Tank makes for bettas. Your Tank is also too small for Corydydoras, as its only a 40liter and they should be Kept in 80l+ (so 20 gallons min) (ootimally. I have Kept them in q5 gallons in an exclusive cory tank) However they shouldnt die due to it. I dont know about Standards in the US, but It just isn't enough space long term as the Tank is planted pretty heavily. Feed them well, do water changes, maybe rearrange the plants so they have space and they would definately aoprechiate oxygen and heavy flow, which your betta sadly doesnt.

 

Didn’t see the 40l/10g. This happens a lot. People read that corys need to be in groups of 6. Then buy 6 for their 5 and 10g tanks and they die. For a 10g 1 or 2 no more. Just not enough space for more.

 

Didn’t see the 40l/10g. This happens a lot. People read that corys need to be in groups of 6. Then buy 6 for their 5 and 10g tanks and they die. For a 10g 1 or 2 no more. Just not enough space for more.

Simply not buying Corys for a 10G is a better option IMO.

 

Simply not buying Corys for a 10G is a better option IMO.

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