Tigermouth and Redtin fin

[FichFry]

Im not sure how to put this but here recently I've notice that
my Tigermouth and redtin fin have been eating the poop of
the Algae eater. I feed them 2x a day, but they continue to eat
the poop. Could they be lacking something or is this nomal.
I clean the tank once aweek. Any help would be great.
Thanks

 

[Jen]

Are they deffinately eating it? Or are they sucking it in and then spitting it out?