Fish on its side

[Lofus]

I did a 5% water change just because I had some made up and ready to make-up for the water lost through the acclimatisation process.

I question if there something was released because I only scratched the surface with a newly added rock. As well, the smaller fish seem unaffected. If there was a contamination issue I would expect the smaller fish to suffer first.

The skimmer is still pulling the same amound of gunk out as normal.

Am I wrong in my thinking?

Jim