Crushed Coral Amount Per Gallon?

So last night I put the 120# of live sand in my new 75 gallon. Its looking good slowly clearing up the cloudiness and the filter is working great. I originally thought I would use live sand and crushed coral so I had also ordered 80# of coral. The 120# looks like plenty already. So obviously there is only one thing to do.....I NEED another tank! (I know that's what you were thinking too.)
If I set up another tank using the 80# of crushed coral, about what size of a tank would I want? I am considering a corner back tank or a regular shaped tank. Ideas?

Another question to add. Would it be a good idea to still use some of the crushed coral along with the sand to buffer the water in the 75? It will be FOWLR tank. Thanks!

 

The new tank might be set up as brackish water. I have had a brackish tank before with some spotted scats and spotted puffers and it was really interesting to look at and also really easy to keep. Brackish fish don't seem to be very picky. I gradually raised the salinity to 1.021 (thru a few water changes) and my fish got much brighter in color and did quite well. I miss having a brackish tank set up : )