My husband gave me three young pimelodus pictus a week ago as a gift. Two are acting normal, the largest is not. It seems lethargic, not eating (two days now) swimming aimlessly or sitting at the bottom of the tank. No visible signs of disease or damage. Water was pre-treated with ich treatment as a preventative measure when first introduced to tank. Any ideas on what's wrong with the little guy or how to help him? (Not a community tank...only three fish)