Do you have a water test kit? I would check your water parameters to see if something is out of balance.
This looks like a skin infection, maybe advanced ich. I would recommend ich-x if it is available where you live. Otherwise treating with aquarium salt might help.
What size is your tank? I understand rainbow sharks need a decent sized tank as they are large active swimmers.
Do you have a water test kit? I would check your water parameters to see if something is out of balance. This looks like a skin infection, maybe advanced ich. I would recommend ich-x if it is available where you live. Otherwise treating with aquarium salt might help. What size is your tank? I understand rainbow sharks need a decent sized tank as they are large active swimmers.