[helgymatt]

I picked up these rocks at a local lanscape supply yard.
I'm not sure what they are or if I should use them in the tank.
From their website it seems they are either sponge rock or holey rock

Sponge rock...
http://www.rhinomaterials.com/photo_gallery/23.shtml
http://www.stonequestinc.com/images/spongerockboulders.jpg

Holey limestone...
http://www.southweststonesupply.com/boulders.htm
http://www.southweststonesupply.com/images/boulders/HoleyLimestoneB601.jpg

Anybody know anything about this rock or where it comes from?
Would it be safe for my tank? I took them to the car wash and they had a lot of rust on them that washed, and washed, and washed. I think I got them pretty clean. And no, I didn't use any soap on them! I hope they wouldn't turn the water rusty.
I would like to use them in a iwagumi scape.
Here are the ones I found...

 

[helgymatt]

Didn't get any fizzing with vinegar...

 

[helgymatt]

People like this hardscape with these rocks? Suggestions welcomed before I do the plantings. Whats in there will be coming out and I'll be planting hairgrass, blyxa, and HC. Maybe a few other things.

 

[helgymatt]

Why only three rocks?

No I havn't tested the GH and KH. I'll test after a few days...just did a big water change. Not too worried about heavy metals because I do weekly 50% water changes.