metalic sand

[Zerandise]

I have an odd one....

I got some substrate off a guy as it was older and wanted to add it into my sand for seeding. All seemed fine.

I am now getting small flakes drawn to the magnet on my algae cleaner. Doesnt seem to be much but some is enough?

I am thinking i should just break it down and start over again. anyone else have this happen?

the shavings are jet black by the way. and so very very small.