The differance may be in part due to Domestics vs wild cought IDK. My Discus were wild cought Heckel and the Angelfish were wild cought Scalare. Perhaphs domestics would behave differently however I have no experiance with housing domestic strains together. IME wild fish need more space are more cautious and are not used to feeding with other species on top of them. In Heiko's artical he mentions 40-50 us gallons per fish (Heckel) so eight fish would require a minimum 320 gallons for Discus alone not including the increas for each additional species. This may push the rqauired capacity up to and beyond the 500 gallon mark. Which doesn't appear to be what is shown in the picture they used in the artical so IDK that tank looks way over stocked for my liking but perhaps in that concentration it works. Do to the small confines of our tanks as compared to a river system I don't think we are compairing apples to apples. Adjustments for this have to be made. This however is my observation and experiance. Either way it's an interesting exchange of opinions.