Everything I've read about Clown Pleco is they are very peaceful but territory-aggressive with their own. When I had my Clown Pleco I also kept other bottom feeders with no issues. These were in tanks at least 30" long. Going by species profiles/studies, they are not aggressive toward nor do they kill other species. Unfortunately, too many times people on forums see a fish opportunity feeding on another and assume they killed it.
I have also read in a species profile you need a red or blue light to see these nocturnal fish and to only feed at night.
According to a catfish-only site, they are wood-eating so the tank should be decorated with several different types of driftwood. "These fish really like to have something to chew on. Squash, cucumber, and other vegetables should be readily available to them (yams are a favourite). Supplement two to three times weekly with frozen foods."
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Hope this helps you.