Those guys can be very territorial and harass the other fish even if they aren't bottom dwellers.
When I had my adopted and older Red Tail Shark, she was a really awesome fish. I think the older age was good because she was mellow. Bossy but not hurtful or aggressive, but sometimes in the other fishes face and they all moved aside or went the their way and it was peaceful. She died at around age 8 or so. (~6.5 inches long)
After awhile I got a couple adoption Rainbow Sharks (also in my 72G) They both were pretty aggressive (around 3.5ish inches) even with a ton of places to hide lots of stones DW and a race track which is what I called the spaces all around the perimeter of the tank, and the swim routes in the bottom 1/3 to 1/2 of the tank like a figure 8 swimming space with alternate routes for the other fish to escape.
This was a very planted tank with large DW mature amounts of Anubius varieties, Java Ferns and Bolbitus, with many stones.
One seemed to harass the other quite a bit and one Rainbow shark disappeared. Then the remaining one just doubled the aggression to the other fish in the tank.
I had a couple 2-4" Clown Loaches, a pair of Bristlenose Ancistrus, and some Cories. For the bottom of the tank.
The RS just made it his mission to butt into the other fish and especially chase them around all the time for the fish around the bottom half of the tank. Including The groups of Neon, and Green Tetras and Cardinals which hung around the mid section of the aquarium. It made a very upset tank and I rehomed the RS when I changed the tank's stock around.
Even after moving a few things around in the tank which can help change aggressive territorial behavior, no luck with him settling down.
Unfortunately I can not share a good outcome. I was sure it would settle down eventually but didn't. They sure are beautiful though.
If I were going to think this through again to keep one, I think it would kinda need to be the main bottom fish, with upper half of the tank fish like Giant Danios, or I had 12 Congo Tetras which seemed to be less bothered by him. Endlers or Endler-Guppies (not the long flowy tail kinds), Neon Green Rasbora aka Microdevario Neon Green Kubotai, or other upper fast moving fish.
Hopefully someone who does have success can share the secrets! I am interested to know.
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves