I have 4 otos (the mini ones that get max 2 inches) and I noticed that two of them have a slightly greener tint than the other two. I have been supplementing their diet with some seaweed and I wondered if like how an overdose of carrots (beta carotene) can give a person an orange tint, if the seaweed can tint them green a little bit. They don't seem any worse for the wear, I was just curious. To be clear, I'm not adding a huge amount, but these are little guys and I suppose it wouldn't take much to tint them. I started adding a bit of seaweed in the tank plastic plants to make sure they had enough food since they made short shrift of the tank's green algae. I've tried algae wafers (the rest of the tank piggies get to it too fast), spinach, and cucumber. The otos don't seem to care about any of the veggies I try to acclimate them to, but they found the seaweed and have been nibbling on that. It is possible that it is just part of their coloring as they mature a bit or maybe it is an indicator of who has been eating the seaweed, LOL! I'd love to hear some thoughts from other otocinclus owners.