The water you will be supplying this tank with is going to be very important. Especially when you're dealing with 900 gallons of it!
Having problems and fighting your tap water, is never a very good idea.
Stocking choices. Alrighty then, based off of what you have put up that interests you, i can give you some feedback already!
- Geophagines: I would not mix the two species of Earth Eaters. A dominant male (probably emerging from the smaller-growing Tapajos group) will emerge and may wind up spawning with females from the other group. Plus, the G. winemilleri are a pretty sensitive species of Earth Eater. This species originates from Black Water habitats, and water that gets above 7.0 in PH in the tank will quickly lead to stress in this species. The Red Headed Tapajos, coming from a mix of both Black and White water conditions in the wild, are bit more adaptable to higher water PH conditions. ALL Earth Eaters are highly sensitive to Nitrate levels in the water. Anything above 20 PPM in the aquarium will almost certainly lead to all kinds of problems for those fish.
- Andinocara: If you want a milder aggression tank, I would just go with the Blue Acara, Andinocara pulcher
. A single Green Terror, Andinocara rivulatus
, will probably spawn with the Blue Acara's and may even put a beat down on those smaller, less aggressive fish in a display of conspecific aggression. These are problems easily avoided by stocking with only one Andinocara species in the tank.
- Red Shouldered Severum: I would add another 2 to 3 more individuals to the Heros sp. 'Rotkeil' group. In larger aquariums like yours, these social Cichlids will look very nice when kept in larger groups.
- Throw out the Threadfin acara, Acarichthys heckelii
, and go with a REAL centerpiece Cichlid for this tank! I'm gonna recommend the good ol' Chocolate Cichlid, Hypselecara temporalis
for your aquarium, because they are a large growing, peaceful species. (These easy-going 'budfies', can grow up to a foot in heavy-bodied length!).
Another suitable centerpiece Cichlid choice would be - of course - the good ol' tried & true Oscar, astronotus ocellatus
. In a really big tank like yours, one of those is definitely sure to impress. (And besides, 'Oscar6' would probably be pretty dern upset if I didn't recommend this eponymous New World Cichlid species for your tank.