Platy strange poop

[Turtle71]

so I moved my fish (Platy and Cory) from my 10gal tank over to the new (used) 75gal tank after the water parameter were great and the temp ok.
After 24 hours all Platy had 3 inch long dark poop and all at the same time. After that they all have white long stringy poop.
The old tank owner said he didn't have any disease in the tank in the last five years.
I am confused now and don't know how to go about it.
Any suggestions? Could this only be stress from the move?

 

[Kittykat364]

Have you fed them something different in the past few days? Sometimes my platies have different poo after I feed them BBS, egg yolk, etc.

 

[Turtle71]

Have you fed them something different in the past few days? Sometimes my platies have different poo after I feed them BBS, egg yolk, etc.

No I fed them exactly the same. But it seems to be better now...the pooping. Maybe it was just the stress and the move to the new tank. Everybody seems to be very happy. They're swimming around and having fun. I decided to give them a diet day today and see if that is fixing the problem. The poop is thankfully just dark again and not as much anymore.
Just let them poop out whatever they have to