The common or blue ram (Mikrogeophagus ramirezi) in any of its varieties needs warmth, 27-30C/80-86F, and that is where finding suitable tankmates takes some thought. The rams will be better in the upper half of the stated range, but many of the "tropcal" fish we keep will find this very problematic long-term. Corydoras should never be above 27C/80F on a permanent basis, but much lower as Colin noted.
Neon tetra (Paracheirodon innesi) is one of the fish that will not last at higher temperatures; they prefer it in the 21-25C/70-77F range, and mid-range would suit them and cories.
You can keep a solitary blue ram, with warmer water fish such as cardinal tetras (Paracheirodon axelrodi) or the close relative the green (false) neon, P. simulans. The latter is actually a very good match, as it can be found in watercourses with a temperature that can surpass 35°C/95F (Campos, et al, 2017). This brings us to the other parameters though, GH and pH, as these fish have some very exacting requirements.
A pair of blue rams would be interesting, but the fish must select their mate. Any male and any female we put together will not necessarily bond, and that spells serious trouble within a matter of a few months if not weeks, with one fish left alive. I can explain this if asked.
