What is the best way to develop (pump up) a flowerhorns hump?
I heard two contradicting stories; 1) raise only one in a tank and 2)
raise a few flowerhorn in a partitioned tank to train its aggression.

Ideally, the bigger and deeper the tank the better. But, a lot depends on the genes of the fish. In order to fully realised the kok, the tank has to be at least 30 gallons. As for the aggression part, you can actually place a mirror beside the tank. Good luck !

As Jason put it, it all goes down to the genes of the fish for hump. The minimum water depth should be 15 inches.
Both of your stories were right:
1) 1 tank + 1 fish + 1 mirror.
2) 1 tank partitioned + 2 fish (1fh & 1parrot)
Hope that helps....

use an air pump............jus joking
genes!!!full stop
no use for answer 1 or 2 if the fh has bad genes

does food also make a difference?

Food plays a role as well, but importantly is the genes.

You would laugh if I tell you what I had been feeding my flower horn....Whatever my family eats: Bread, steam rice, tiny pieces of raw beef and chicken, when i was preparing dinner, and goldfish (scales only) left over from Arowana swallowing the goldfish. When my FH reached 4", his head begins to grow and changed into an extremely aggressive fish. within 2 weeks, his head reached the size of a ping pong ball. So food plays a very small part in my FH's head grow. Another key thing I think is water quality. I have 2 powerful eheim professional filters (each can support 158G capacity) in my 180G tank and I still change 10% of water weekly. So for me...Gene, Gene, Gene.

sorry for the stupid question but what does KoK mean?

kok- nuchal hump..

when the head grows out- water heads or hard heads

hehehe.... everyone wishes they had a big kok
just like me.... oops i ment like top grade flowerhorns l-l0l_l

hello there friends.i have a thaizz i bought last june 9 and im in love with him because he already has a kok would u believe that a 2 ins fish had that.i want his kok too be masive what can i do? pls help

hope the advise will work out for you

you can't tell or do anything to a fish in order for him to have a massive kok if he doesn't have one. all you can do is take care of your fish and see how he turns out. if there is a technique in making all fh kok massive, then, there will be no more fun in raising them at all.