I would let your tank mature for another three months at least until a decent biofilm has grown over everything.
These guys love fresh green algae, so if you don't have any, they'll get pretty hungry. Some people grow it on rocks outside for them, in a bucket of watering a sunny patch. I also feed mine blanched courgette mainly but experiment with other veggies. They do eat algae wafers and other catfish pellets but those alone make a pretty rubbish diet for them.
They are very picky and can keel over and die for no apparent reason even when you've had them months. They do best in a really established tank. Sensitive to water quality. Like to be in groups, so aim for at least three in that size tank - yes they need larger groups, but that's a small tank, and you'd need to feed them a fair bit to make it go around. Lots of plants and hiding places - that's not to say they never come out, mine are on the glass all the time, but they like to hide a lot.
If you think you can feed them properly with algae and veg, You could consider a few, but I personally wouldn't add them to a three month old tank.
