Is black poop a bad thing?

[PlatyLady]

I read somewhere that it's nothing to be worried about. I forget if it meant that the platy had just given birth to fry, or had just eaten them. I have no idea where I got that idea from...

This was ages ago, and I can't find anything on it now. Is it a sign of sickness? It was only once and it was this morning. This platy is behaving normally otherwise. She did get 'skinny' a couple weeks ago (no little pot belly like most platies) - she might have had fry, but I don't think she got big enough.

 

[PlatyLady]

Oh.... parameters. Ammonia, nitrate and nitrite are at 0. pH is 7.5. I did a 20% water change yesterday.

 

[tkos]

Probably what she ate. I think it is a big problem when the poop is white.