In nature they are primarily vegetarian, but will pick off tiny fish (especially in the confines of a tank).
They share habitat in Mexico with Poecilia mollies (also primarily algae eaters) , so to me, these would be a good choice, as they are large enough to not be eaten, but small enough to not pose a threat, and will inhabit the higher areas of the tank, fenestrata the lower areas near the substrate.
And in nature fenestratus live in hard, mineral rich water, and those riverine varients will often enter brackish, even sea water , same as mollies (sail fin type are prime examples).
RO type, mineral poor water may not be good choice for them.
When Stakowski collected them, he reported
pH 7-8
general hardness 4-11 dGH
calcium hardness 5 -13 KH
Mine spawned in medium hard water (@250ppm Total hardness) pH 7.6-7.8.
If breeding is your intent, and want to keep fry, medium or large tetras may not be a good idea, as they are consummate fry predators, very quick and accurate hunters.
I just had a pair of Andinoacara spawn in a heavily planted 180 gal, it contains some Roboides tetras, each day the tetras methodically reduced the free swimming fry school, until within less than a week there were no more fry.
My intent was not to save fry.
