flowerhorns' colour became dark and activeness is reduced..They remain scared nowadays..help!!!

[pop.k]

i have two flowerhorns partitioned in a 2×1 ft tank..Both were fine for a week or two after they were kept in the partioned tank..But after two weeks their colour started becoming dark nd now they have lost their true original colour and have became much darker..can you tell me what is the actual reason behind it?also i will be glad if someone tells me the gender of both the flowerhorns..one is a long body and other is the box body...thank you i will post before and after images..

 

[fisheatfish]

Colors on them looks ok. Could be water condition. There may not be enough water flow passing from one side of the divided tank to the other leading to poor filtration & uneven heat distribution.