There is so much about this hobby that is built around something's that were anecdotal at best and pure deception by keepers trying to keep their secrets. The myth about ph is just about done but you still get people that will swear that it needs to be at a certain level for certain fish. Most of us now know that a stable ph is more important to have healthy fish. Just look at a store shelf ph+, ph-, stabilizers ro water filters. We have all been in a lfs and heard the employees telling the newbie they need this and that and that other thing and thought what are they saying! and that's just chemicals.
With fish this seems to be at its worst with discus. This still goes on now some of the biggest names with discus still pass along half truths.
as with anything follow the money, as long as the myth stands the higher the price stays if it were widely know that they are easy to raise and spawn the price goes down. Keep the myth going and price stays high.
The biggest names in quality discus are not the local breeders its guys who import them from Singapore, and other Asian countries and Germany they aren't raising these fish and doing the heavy lifting so to speak. They have them shipped half way around the world. If they were as fragile as some would have us believe they would not be importing them.
Its the local breeders (not all of them by any means) that sell their fry that don't always tell the whole story ( there's a reason its call a fish story )
Its in their best interest to keep up the myths I have been doing a lot of research for an article I am writing detailing a lot of these myths and half truths. Most of the so called facts are just what one person said as fact back in the early days and have just stuck and to some is gospel but try and find any studies of scientific fact and there is none.
I have been doing in the last week or so started to research probably the biggest controversy which is do fish secrete hormones in the water that stunt other males. There is lots of people who say they do but try to find a study or scientific testing no one knows of any but they will swear that its true.
This hobby of ours needs to cut through all the bs and stay with facts if it's going to survive to the next generations. IMHO
In short there isn't anyone who can't keep discus the plain info is :
1. keep 1 or 5-6 discus nothing in between (unless you buy a mated pair $175 - $800 +)
2. Do your water changes the larger the fish the less PWC you need to do
3. keep the temp in your tank 84 - 90 the younger the fish the warmer the water.
4. feed them a high quality diet.
that's it in a nutshell not that different from other fish ( other than the few cichlids that do not like fresh water that need aged water)