Hey Robert, I've learnt hard way also and I lost them too for various reasons. I am rebuilding my stock again but here in Australia is very hard to get them. Currently I have two F1 Atabapo Altums. They doubled in size in one month (around 25cm in height now), so what I am doing now must be the correct way. Town water in my place is around 150ppm TDS, pH 7.5. This time I left TDS alone, no changes. Acidity is another story, I lower pH to 4.8 -5.0 max (I use hydrochloric acid in aged water to be used in aquarium). I never add acid directly to fish tank, it will kill the fishes. Temperature is stable at 28 C. Altums have tendency to become sick (bloat, fin rot etc.) and die when pH goes above 5.5 and no medication can fix that. I keep them with 7 corydoras, 5 small discus, and around 12 whiptail catfish (royal whiptail, R. parva and farlowella acus). Tank is 840L 140cm L x 75cm W x 80cm H. I've removed 8 Colombian tetras, they were too competitive for food. It is planted tank with some driftwood. Plant matter is essential for altums, they are omnivores. They eat spirulina flakes, discus flakes, frozen brine shrimp, mysis and rotting water plants. No stress in such conditions, in contrary they challenge each other very often and don't care about my black kelpie dog running in front of the tank. They are very beautiful fishes and if you like bit of challenge they are the ones for you.

Alums come from Orinoco basin not Amazona. Replicating brown water is very difficult when you change 50% of it weekly.