I got these rocks from my LFS, the owners said they are safe for aquarium and growing plants etc. However I didn't manage to ask for the name of the rock. Fast forward, I soaked the rocks in hot water for a few hours, and there were obvious red/orange dust/powder thing that came off. Then I scrubbed it again and soak it in room temperature water, this time round there isn't much red powder. I then tried the vinegar test using black vinegar, but there isn't any reaction. So I assume it will be safe to use, but i was reading around if the rock is reddish, it might be high in iron, which will be bad for fish or shrimps in the future, is that right? The tank has been running for 3 days, and there isn't any red/orange dust or powder in the tank.