I'm guessing from the pics that you are raising an albino strain of BN ? Pleco.
It's been my experience when dealing with albino anything's that there is an inherit genetic weakness in some which makes them more suseptable to disease and early death.
Case in point, the Electric Blue Jack Dempsey cichlid. It is 100% JD but has a recessive gene that provides it with a stunning blue and black color pattern. That same gene deficiency makes the EBJD a much weaker, more fragile fish.