Thanks for the comments.

I have no idea exactly how much rock is in the tank. The only live rock that I purchased was a 50# box of Fiji when I set up my first tank.
Since then I have just purchased base rock from several LFS over the years. I actually have around 30 pounds soaking right now.
Normally what I do is place the base rock in an extra 20L tank that I have, add a piece of live rock and a powerhead for circulation and fill it with water from water changes for about 3-4 weeks.
I don't know if it is totally necessary but the rock usually colors up after about a week in the tank with no effects on my parameters.
If I had to guess I would say maybe around 180-220 pounds