What size aquarium is this?

Well just to refresh with tread, i added my lone yellow lab and 2 rainbow cichlids. I know that mixing cichlids is not great but i tried to match the aggression levels and keep the adult size of each fish under 4-5 inches. So far things are going well, 5 months in. I just saw that someone remmended a single discus would that have worked? Just curious.
 
Nah...They like to be in groups of at least 3-5.
 
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