How many cardinal tetras would be needed for them to feel safe and confident among 6 corydoras?

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Johnny420

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Hello guys, first aquarium I have ever done. I cycled it for 16 weeks and used fish food to get it going, until 3ppm ammonia (dr tims) was fully gone in 24 hours. Tank size is 125l with six corys and five cardinal tetras. It was supposed to have been 6 tetras but one was already dead in the bag when I got them back home. I put all six corys (peppered) in at once last week and had no ammonia or nitrite spikes. So yesterday I thought I would get the tetras I planned on getting. I am thinking I need about eight of them or something now. Six is the minimum they say, but with six corys in there I'm thinking I need more of them to feel safe and not be so shy. The five I have seem pretty shy. They do seem to be sold a lot smaller than the cardinals I see most other places, so maybe that has something to do with it. These are just 2cm.

Tetras and corys seem to be fish that are in the same tanks a lot from what I've noticed. Hopefully someone can help me out before I buy more so I know how many more to buy.


Thanks
 
I'd get a dozen at least. They're not incompatible, both types keep to their own and move mostly in different levels of the water column. In my own experience I have 13 tetras (neon) and 6 cories in a tank the same size as yours, and they are doing well. I'd go for up to 20 neons if I could, but I'm holding off on that for other reasons.
 
Welcome to the forum btw 👍🏻 and if you don't have any, you'll make them all happier if you have live plants, plus they help keep your water clean
 
Hi and welcome to the forum :)

16 weeks seems like a long time for a tank to cycle.

If you have cycled a tank, you can add all the fish at the same time after it has cycled, because the beneficial filter bacteria is there ready and waiting. If you ever decide to get another tank, you won't have to cycle it and can simply take half the filter media/ material from the established tank and put it in the new tank.

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All tetras do best in large groups and naturally occur in groups consisting of hundreds or even thousands of individuals. In an aquarium, the minimum number is 10 and preferably more.

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If you post a picture of your tank, we might be able to offer ideas on how to improve things so the fish aren't as stressed.

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Avoid buying fish that have just come into the shop. Ask the shop when they get new fish in and buy fish the day before the news ones come in. Doing this means you get fish that have been in the shop tank for a week or more and they will be less likely to die in the bag.

You can also ask the shop when they do water changes and buy fish the day before they do the water change. Again it's less stressful for the fish.

Watch the shop assistant when they are catching fish. if they are chasing fish all over the tank and it takes more than a few seconds to catch them (5-10 seconds is ok but a couple of minutes is bad), maybe see if someone else can catch them or come back another day.
 
Thanks @outofwater I do have 2 x hygrophila corymbosa by tropica at the back. They're getting pretty big already and they're only 3 weeks old. I started seeing new growth after just 7 days. I put some tropica plant substrate underneath the sand when I first got the tank set up. I decided from the start I won't use fake plants tbh.

I think I will go with 12 tetras as you say. I think they would be more energetic with more. They're certainly not ill. I think it's a safety in numbers thing tbh.
 
Thanks @outofwater I do have 2 x hygrophila corymbosa by tropica at the back. They're getting pretty big already and they're only 3 weeks old. I started seeing new growth after just 7 days. I put some tropica plant substrate underneath the sand when I first got the tank set up. I decided from the start I won't use fake plants tbh.

I think I will go with 12 tetras as you say. I think they would be more energetic with more. They're certainly not ill. I think it's a safety in numbers thing tbh.
I started with 12 back around Christmas last year. 5 died within the first 2 days, just bad batch due to bad weather/season to get fish here. Waited a bit, tried to get numbers up to 12 again about 2 months ago I want to say, and all 5 died again. I almost gave up on them, but about 2 weeks ago decided to try one last time. The weather is nice and stable now, the fish looked noticeably healthier this time at the store, so I bit the bullet and decided on 6, to make the third time a charm with "lucky 13". I'm happy, they're happy, and I've seen the difference that the increased numbers have brought on: the neons are now much more outgoing as a group and patrol the entire tank, whereas when it was only the 7 initial survivors they tended to be a bit shy, stay in the background unless it was feeding time and generally seemed skittish and looking for cover in the plants. Now they constantly shoal, chase each other and come up all the way to the surface when it's feeding time. Definitely go for a dozen, and if you get some 20 or so, it'd be even more beautiful. Your cories will be just fine, for the size of the tank you have they all will be perfectly fine. I'd even suggest getting 4 more cories, those are also happier and more fun to watch in numbers.
 
I put more tetras in (all cardinals) and seen a huge difference in their behaviour around the cory's. They don't act scared at all, like scatter about or swim away fast when a cory is nearby or coming towards. That was happening when I first got them. Now they will even swim around and next to the cory's while they're grouped up on the bottom resting.

So now in the tank there is 12 cardinal tetras and 6 cory's. It would have been 14 tetras but when I brought the rest home, 2 died but tetras are very sensitive like that it seems. The cardinal tetras are much bigger now. They were tiny when I first got them. I am intending to get more fish but not sure what yet.
 

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