Cardinal Tetra small group

Hey there! I'm fairly new to the hobby, and three months ago someone gave me their aquarium (about 5 gallons). In there were 4 cardinal tetras. I put them in a 15 gallon with some guppies, and I've been dealing with a few diseases for the past couple of weeks. The cardinal tetras were doing perfectly fine. However, last week one of them passed away, and 2 days ago another followed. I noticed the remaining two hiding in the plants a lot, and I haven't seen them come out to eat either. They don't look sick, and neither did the ones that died, so I wonder if this behavior is coming from them being in such a small group? I know they're schooling fish. Because of the sickness, I wasn't planning on buying any more fish for the next couple of weeks because I want my aquarium to run properly first, but do you guys think I'm going to need to add more tetras (perhaps neons?) in order for them to survive? Or is there another disease going on that I can't see?

 

They do better in groups, as you mentioned, but I doubt that's why they died, and even if it was adding neons wouldn't help since most fish will only shoal with the same species. There's something else going.

 

I have 2 cardinals. They are the last of the origional school. They hve been only 2 for more than 2 years and they just hang out with the neons. You dont need to buy more but if they are still young maybe you should get some more or rehome them. Mine are old so im not increasing the group. It isnt urgent though. They shouldnt die if they are healthy just because of a small group. Wait until you are ready and then decide.

 

I'd rather buy new cardinals than neons (read the numerous diseasethreads about those). Neons might do better in a 15G than Cardinals though.

 

I currently have 3 cardinals left in a 20, they are doing quite ok. More would be better, but since I have an unknown parasite ravaging my stock there will be no new fish until they either all died or none has died for more than two months.

Anyway, the three left are not that shy. I guess it's mostly the moving to a new tank that causes the shyness in yours.

 

Thanks for the quick replies! I believe they are already a little older (+/- 2 years), and when I put them in the new tank a couple weeks ago they were very active and schooling together (with the 4 of them), it's only since the other two passed away that they've been acting this shy. I haven't seen them come out to eat for at least 2 days now.

 

Shade the tank a bit and give them some time.

I lost some of mine also likely because they were old. The first batch of three came from a neighbour and they were all between 3 and 4 but got stressed a lot by an algae eater (decimated them 12 down to 3 in a months or so) before they were rehomed to me. When I accidently introduced that strange parasite (From wild-caught Otos, from what else...) those three got it first. Two died of it, the third actually survived and jumped over night two months later, when I had no cover on. *facepalms*

 

I tried to shade the tank, but sadly one of them passed away yesterday, and another one just now. Very strange how they went from happily swimming around to this!

 

Welcome. What are your water parameters and how often do you perform water changes. Also what temp are you keeping the aquarium water at.

 

What temp is the tank? Before buying more cardinal I think you should make a stab at figuring out why they died. Cardinals are one of those fishes that really prefer clean warm water. I have 26 or 27 in my tank and i know when something is wrong by how they behave (of course having the angel swim too close to them is one of the things that tell me something is wrong ). I've lost 4 the past 12 months and 3 of them was due to introducing a sick fish (maybe i should feek lucky it was only 3). There really isn't a good reason for established cardinals to die unless something is wrong and it sounded like those 4 had been well established.
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As others have noted they feel uncomfortable unless they have more of their kinds to keep them company (it isn't the company as much as it is the feeling of being 'safe' - you know safety in numbers).