What happened to Marvin?

[Salty&Onion]

If you give away any of the fish, don't replace them with anything else as your tank's already full of fish (overstocked). I agree on the temperature, it might have affected him as usually rams require higher temperatures and if you have hard water, this could also have effects on him as rams are soft water fish.
Also, mixing rams is a very, very bad idea.

 

[utahfish]

I am at 27.5 c which seem to be within the range for all the fish in the tank.
Bolivian ram is very chilled... so different than other rams which are active.

81.5 is a bit toasty for Bolivian Rams, they do better in high 70s and German Rams do better at 82 or above.
When one runs higher temps than fish have evolved for it accelerates a fish metabolism and growth and lifespan higher temps also decrease available oxygen levels in water and increase propensity for bacterial infection. German Rams have evolved to livr in warmer temps Bolivian RAms have not. Also Bolivian Rams get bigger than Germans and once it gets a little older will most likely like all cichlids will form a territory and will defend it causing stress with other RAms and possibly the Gourami as gourami are territorial as well. While Gourami and Rams inhabit different areas if tank gouramis will venture into bottom where RAMs reside.
Causing aggression or stress, increased stress leads to disease disease leads to death.
81.5 is also way too warm for corydora, they like mid 70s. Cardinals and rummys can do ok at 80.

 

[PheonixKingZ]

Sorry to hear about your fish...

It could have died, and got eaten by the glass catfish, or another fish. (Or maybe the cleanup crew, if you have any snails/shrimp)