I used to have them as well, and a 150 gallon aquarium with Chiclids. Just a suggestion, but never do a complete water change, only maybe 1/3 at a time. I would put my Siamese Fighting Fish in a plastic bowl or vase with 2/3 or the original water, and clean their original vase, rocks etc. I wouldn't scrub the algae off the rocks, only rinse them to get the poop off, so there was always some algae still in the established new home. It could be shock, hopefully he'll be okay. What color is he? I had a blue one and a red one, in seperate containers of course, but across the room from each other.