Substrate gone wrong?

[Reesestapper]

I used organic potting soil under a layer of rock i bought at the pet store. Problem is, somehow some of the pot soil, ended up on top. Is this harmful? And can i add fish?

 

[Rivercats]

Just carefully add more of your cap over it. Also be mindful when planting. How deep is your cap over the soil? An inch and a half is a good amount to cap with over soil.