OK Here is usually most experienced Corydoras I think would agree.
For the well being of Corydoras, you should keep as big group as possible your tank can handle the bioload.
And they would be much happier of their own specie than mixed. If it is kept mixed, there are several issues you probably need to address.
Since not all Corydoras have same optimal water condition. Some prefer more cooler or higher temperature than others, some prefer more acidic or alkalline., etc. Even their size can be a problem. Some get bigger than others and some are more active and out-compete the more shy slow one.
Also if you have mix of small number Corydoras, you are running the risk of Corydoras hybridize. Which is not really a good thing for most serious hobbyist mind.
So they may group together for necessity of defense mechanism but if you like your Corydoras, you should really stick to 1~2 kind per each tank. And each should be 6 and more.(some may suggest less and claim they are happy and doing fine with 1 or 2, but usually those people never kept them in bigger group. And it will make big difference. And you will see more natural behavior if they are kept in bigger group. In the Nature, they are known to live in hundreds or thousands.) Especially if you are looking more rarer Corydoras, you should get big group at same time, otherwise you never know if you can get the exactly same species ever again. Sometime they can be really tough to correctly identify for normal hobbyist.
Of course, the tank should be well cycled before you bring any fish home. Do some research about the particular species you like before you get. So the tank condition would be ideal for them. That would make your fish happier and live longer for you to enjoy. Some Corydoras are known to live up to 15~25 years if they are kept in right condition.
BTW, C.Panda is usually known as delicate and fragile. And they do need more tender care of high water quality IMHO. So you may want to start with more hardier Corydoras first.
And they also should be kept with some peaceful tankmate only. Usually small Tetras or Rasbora would be good. But some Barb or some Tetra can be fin nipping. So you need to do some research about tankmate also. Of course, you can always keep only Corydoras in the tank. That is most of mine tanks are. If they are in big group and happy, they would be active in all part of the tank although they are suppose to be the bottom dwellers.
Anyway, good luck. I hope I covered most about keeping mixed Corydoras vs keeping big group of same species.
- Frank
