Unfortunately only one Cory right now, the pet store had 3, so I bought all three, but didnāt look at them til I got home and put them in the tank. Two turned out to be some sort of upside down catfish??? My fault for not looking closely. I asked the owner to order more, so hopefully will get 4-5 more corys. I feel slightly limited with 16 gal, and donāt want to overcrowd. Will probably make 1/2 the tank sandy at some point per your recommendation. Or I could sell the one Cory back to the pet shop, and go all tetra or something... got some thinking to do...
Hm... A lot of problem solving to do here.
Tetra tanks are very pretty, but can be a little lifeless since they have less character compared to fish such as catfish. If you go down this route, I'd recommend a school of rummynose tetras. They're very lively and fill the tank with their colour.
I wouldn't say that the cory/upside down catfish mistake is your fault - particularly if they were all labelled as corydoras in the shop. It's always disappointing finding out that you were sold the wrong thing, but on the bright side upside down catfish are lovely and full of character. They
do need a bit of wriggle room, but my two were just fine in my 13G tank temporarily.
If you're already emotionally attached to the cory, try and find some more. I'm assuming they were all supposed to be julii corys? You can order fish online, but be prepared to spend a good amount on shipping as shipping live fish is costly and you will need 24hr express delivery to ensure their survival.
Of course, if you're happy giving the corydoras back, go for it. You can easily find some more since they're pretty much in every fish shop. Same with the upside down catfish, especially if you're not a fan of them. Personally I adore them.
Saving up for a larger tank may be beneficial, too. The footprint of your tank is a huge factor in how your fish will thrive, so make sure to keep your eye on a nice tank with a good amount of floor space. No BiOrbs or nano tanks - particularly if you're going after fish that get a little on the larger side like corydoras do. A good size for corys is
at least 20 gallons, so you should look for something around that size if you're looking for a bigger tank. I would definitely advise it if you want to keep the corys.
The reason why they need sand is to protect their undersides and whiskery barbels, which they use to help them find food. Sand is much gentler than gravel, and as such will prevent scratching or chafing of their delicate little tummies.
Hope this helps. Let me know what route you go down, I'm always happy to offer more advice if needed. And don't forget that there are hundreds of other members always willing to help out.