Just recently my labeotropheus trewavasae has been acting oddly hes been going to the surface of the aquarium taking some air and then trying to swim downwards he always seems to be swimming in a vertical position and whenever hes not eating he does this. I know that could be an indication of under-aeration of the water but the other fish aren't doing this and I always keep the tank properly aerated. Your help would be greatly appreciated 
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