Yes. Freshwater rocks tend to be smoother than reef rock which doesnt allow for proper bacterial colonization. Also freshwater rocks may have heavy metals in them that can leach out over time such as copper
Many rocks depending on their makeup can leech heavy metals, silicates and even more harmful compounds. The problem with river or quarry rocks is that it's a big unknown where they came from and what's in them, could be iron or copper or like quartz that leaches silicates and could feed diatoms. Not to mention they aren't the best media for bacteria as they aren't nearly as poreus as reef rock. Best to avoid problems and leave them out.
I built a few frag racks last night for my first Coral coming tomorrow.They are getting knocked over by my Power Heads..I'm trying to get them weighted down.
I guess I'm a tad lost..I have my first Frags coming tomorrow.Plan is to dip them...then put them on some racks I built and hopefully figure out where they wanna live...light/flow is my first thing I wanna figure out.
So your question was asked because you wanted to eimmweigh down you frag racks with freshwater rocks I'm asusuming... I also assume your tank is cycled with proper rocks typically used in reef tanks (i.e. live rock, dry limestone rock). If so, any reason why you dont mount the frags on your live rock?
If the frag rack is temporary until you find the time to mount your frags on to the live rock, you can use your magnet scraper with a zip tie tied to rack and wet side of the scraper.