These are very much like Gymnogeophagus, being from southern South America, a sub tropical climate, and appreciate a bit of a cool down. I keep A sp. red ceibal, which is arguably may be a locality variant of oblongum. In summer they take temps in the 80s and 90sF, in winter temps in the 50s. When I tried to keep them at constant tropical temps, they had shortened lives.
A 55 has been sufficient for mine, I don't use a heater at all, and keep them with Gymnos, and Uruguayan pike cichlids. My room temp is mid 60s
My largest male reached about 7", but they start breeding at very small size 2+" for females, males a bit larger.
By the way, I have found them to be great pond fish, I have them in my shallow 1500 gal pond late April thru early Oct in Milwaukee where temps get into the 40sF at night and 90sF day. They will spawn in 6" of water, fry live off algae, I usually bring in 80-100 fry in fall along with adults, to take to our local aquarium society auction.
They have also spawned in an outdoor 50 gal tank choked with algae.
The sun and diet of algae seems to really bring out their color.
In this pic you can see a group of 1/2" fry to the right, if you look close.
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Nice blue on yours, the "ceibals" don't have that hue, probably a location difference trait.