Should I Use These Rocks?(are They Safe?)

Recently, I collected some rocks from a local stream. When I brought them home my grandpa made this comment about them being “no good”. He said the stream they came from was used for mine run off or acid water. When I was collecting them I saw snails and crayfish living in the stream.
The rocks do have some red/ orange on them that looks like sulfur.
I did a test where I put one of the rocks in a 3.5 gallon bucket.
I used tetra 6 in 1 strips to looks for a change in gh, kh, and ph.


Here are the results: left is from the bucket with the rock left in there for 3 days,
Right is my water straight from the tap, below is my water left sitting over night(my ph drops without a buffer) the only thing I notice is that the gh changed slightly(went up). Also it held the the ph.


L-150ish gh, 40ppm kh, 7.0 ph. R- 75 gh


75 gh, 40 kh, 6.2 ph.

I think if the acid run off had affected the rocks the ph should’ve gone down right? Since the run off is sulfuric acid. I don’t mind that it buffered my water because I always have to add to mine to keep my ph up. Usually cichlid substrate, crushed coral or one of seachems buffering products.

Do you guys think the rocks are safe?

 

If the stream has crayfish the water is good. They are usually the first thing to die off even before fish.

 

If the stream has crayfish the water is good. They are usually the first thing to die off even before fish.

Thanks, that’s why I included that, I personally think they’re fine. I just wanted some reassurance. My grandpa freaked me out a bit saying all my fish would die.

 

They look all silicium = safe

 

Those look like field stones so I'd use them.