Well, I don't know specifics. That's the problem. A lot of Asian breeders are keeping altums in very closely-controlled systems where water is monitored constantly. I've seen videos of it online. They won't reveal exactly what they're doing, or if they're adding something, but I know the hardness and pH are kept quite low. When it comes to things like wild heckel discus, males will readily cross with domestic females but it's hard to find the trigger to get a wild female to spawn. Altums will pair up but rarely breed. In both instances, it's always been assumed that pH and/or hardness was the trigger. pH and hardness also play a factor in other aspects of breeding, like the sex ratio of a spawn, viability of the eggs, etc. There are a lot of ways to artificially alter the water and some people have figured out triggers. Discus breeders used to play around with small amounts of muriatic acid, if I recall correctly. There was another chemical that used to get used a lot, it was a common household chemical, but I can't remember what it was now.
Anyway, the point is, I'm sure these trade secrets get passed around and tried on all the various fish that are labelled hard to spawn.
