Originally Posted by nicolaas
What about Length 150cm,width 60cm,height 40cm. that's 360liters/ 95gal.
With respect to the knifefish, this would work well.
A suggestion on the other fish: angelfish would be ideal, a group of 5-7. I would myself leave out the Silver Dollars. For one thing, they are vegetarian, and I strongly recommend floating plants for the knifefish and the angelfish. Believe me, floating plants make a vast difference to both species. But being tender plants, they would get munched on by the vegetarian Silver Dollars.
Angelfish do very well in tanks with substrate-rooted plants like swords, Vallisneria, etc., which is why SD's are not good companions then either. But as the dim light here will make submersed plants difficult, I would suggest a more authentic Amazonian biotope with lots of wood branches and bogwood, a sand substrate, and then thick floating plant cover. This would be very authentic, and the knifefish and angelfish would be very happy and relaxed--which means healthy.
Substrate fish like the pleco, perhaps a couple of Whiptail Catfish, are fine. On the pleco, don't go for a vegetarian species like Bristlenose, since algae will be minimal. The Hypancistrus species are primarily carnivorous, and there are so many beautiful species entering the hobby these days.