Some have suggested that my rock is bad, or has become bad after years of usage.
Anyway, I have a colony of Nuke Greens growing all over one of the rocks, so I went to chisel off a the piece with them on it. Took about 30 seconds to carefully remove their piece from the main rock. Underneath, in the rock itself were tunnels of varying size and all were almost 100% packed full of detritus and sediment. I rinsed the 2" piece that I removed and it clowded an entire 5 gallon bucket, literally couldn't see an inch into the bucket. This sort of stuck home on the idea of bad rock, so I chipped off another small chunk and put it in a container of brand new RO/DI saltwater. After about an hour, I tested it and the NO3, and PO4 were completely off the chart, literally, off the scale. This is rock in the highest flow area in the tank. These tunnels were completely inside the rock, with microscopic access to the main volume of tank water.
So this isn't exactly scientific. I didn't use a huge volume of water to test in, but the fact remains that the rock is obviously leaching a lot of crap bank into the tank. If a 1oz chunk can make a half gallon of water read off the chart, 30 lbs has a lot of potential. I'd be willing to bet that rock like this is pretty much unrecoverable. There's no amount of blasting that could possibly dislodge the sediment and detritus. Even if the rock was completely cooked or dried, it wouldn't remove what's inside. I've read more than one article on overly-porous rock. This might just be the problem with it.