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Can a discus live with an extremely docile silver tip catfish, or will the discus hide all the time?

Don't have much experience with Discus, but I'd be a bit surprised if they hid from the catfish. However, I'm not sure exactly what species your "silver tip" is. There is a catfish often called a silver tip, sometimes called a Bolivian silver tip, or various other names that, while peaceful, presents a problem in that as it matures, it requires more and more salt in its water, until as an adult it lives in a truly marine environment. I've seen a lot of these in the trade lately, so do some research to see if yours is this species. If so, ultimately either the catfish or the discus will need a new home even if they get along great.