my mala has jsut been moved to his very own 75 at 10". He really does look far too small in there at the moment but today i have noticed indredibly agressive tendancies. its a semi planted tank where he has room to hide as well as open areas to wander the substrate. Earlier i walked up to the tank to check the water qualities as it is 2 weeks into its cycle to find him baring his teeth, gills wide and following me arround with his eyes. I investigated only for him to shoot towards the glass, not hitting it but really baring his teeth. My only conclusion is it's territorial behaviour and having only been in the tank 3 days he is trying to stake his claim to the whole thing. Still though; He is only small and acting like that. I would be very worried about tank mates.
I tried my chap with an 11" livingstonii when i bought him home at jsut 6" and within 30 mins he had already wounded the livingstonii. It was a massive wakeup call so i would really recommend leaving him on his own. It jsut seems like no matter how well he a mala behaves with other fish, it is that one day when another fish gets a bit too close...
...if you know what i mean. They have enough character to warrent their own tank thats for sure!