My last batch of arm looked like crunched up larger pieces of coral. It melts and works just fine. I bought a 50 pound sack, so no idea if it said "high magnesium" on it. I find no difference between ARM medium, ARM large or reborn... I just get whatever is cheaper when I need a 50 lb sack again.
I Need to be more clear why change the media to 100 percent Dolomite. I have used a few cups worth but looks like it’s being sold to be used as 100 percent in the reactor.
The only reason I can see to run it is if you have a high magnesium demand and want to try using 1 product. For me I run the coarse Reborn media and Zeo mag. A ratio 90% Reborn and 10% Zeo
Dolomite will work, it just has more magnesium in it. I find any natural media (ARM or Reborn) to have enough mag by themselves and have no reason to use dolomite. You could get too much magnesium if you run dolomite alone - most people mix it with regular aragonite. I used dolomite when I tried some man made calcium carbonate which had no mag or other traces in it.
That probably is not dolomite then... I would have expected a lot more mag. It is probably just smashed up calcium carbonate rock that looks like smashed up dolomite.
I stopped using ARM, the new stuff just doesn’t dissolve like the obvious coral skeletons did. It looks to me like a tub of Pea gravel. I started using their Florida crushed coral sand instead. Works better and costs about 1/10 of the ARM stuff.