Welcome to the forum, and to cichlid keeping! They're great fun, when they're not driving you crazy! I'm assuming that your Red Devil is fairly small at the moment. If it is a RD (can you post a pic?), I wouldn't advise putting any other fish in there with him, as these guys are very territorial, and would likely attack any added tankmates. (S)He will also grow quite large, and rather quickly outgrow that 33 gallon. Long-term -- like within 6 months -- you're going to need at least around 75 gallons to adequately care for him, and even in that size tank he wouldn't willingly put up with company.
Your best bet IMO would be to either trade the tank in for a much larger model, or trade the fish in for something that won't grow quite as large. A couple of Convicts or a Jewel fish come to mind as examples of cichlids that would be OK in a 33, or maybe a couple of Firemouths or Keyhole cichlids. For sure though, that RD will be too much for that tank in a matter of a few months.
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http://oscarsfishtank.com/discuss/index ... ic=22750.0Good luck with your fish. It's a great hobby!