I don't see other substrate fish in the photo, so for the moment the Red Tailed Shark may be "OK" but just remember, no other bottom fish with this fellow in the tank. He will drive fish like corys to distraction, causing severe stress and poor health. Just his being there will do this.
The tank is small for the fish, even though he is "smallish" now he will grow, and in a small space (to him) this can cause even more aggression. This fish has been known to suddenly take a dislike to upper fish too, brought on by unsuitable environment.
RTS is a beautiful fish, no argument there; but as it notes in our profile, this is not a good fish for a community tank (unless as LasColinas pointed out, a very large tank) or for new aquarists. The possible (more likely probable) trouble soon to come is not worth it.