Corydoras

Corydoras are the best-natured fish we sell and among the most commonly kept badly. Two things fix nearly every problem people have with them.

Buy six, not two

Cories are intensely social and behave completely differently in a proper group. In a pair they hide and sit still; in a group of six or more of the same species they forage openly all day, and that is when you actually enjoy them. Six of one species beats two each of three species — they shoal with their own kind, not with cories generally.

Sand, or smooth fine gravel

Cories feed by sifting substrate through their barbels. On sharp gravel those barbels wear down and get infected, and a cory that has lost its barbels cannot feed properly for the rest of its life. It is the single most common avoidable injury we see in this species. Sand is ideal; smooth rounded fine gravel is acceptable; sharp or coarse gravel is not.

They still need feeding

Cories are not a cleanup crew any more than plecos are. They eat what reaches the bottom, and in a well-fed community tank very little does. Sinking wafers or pellets after the lights go down, so the faster mid-water fish do not take it first.

The surface dash is normal

Corydoras gulp air at the surface and absorb oxygen through their gut — it is how they are built and does not mean your tank lacks oxygen. Constant repeated dashing does. And keep the water on the cooler side of tropical: most cories dislike the high temperatures discus and some other fish want.

See also tetras, rasboras and sinking foods.