Curious if you ever, over time, had to add dolomite to the tank. I ask because isn't that a calcium based rock similar to what is put in a calcium reactor. I have wondered whether gravel systems with particulate at the bottom would break down the rock, and in the process bring the ph down to such an extent that it would dissolve the rock. Reactors dissolve arragite/shells at around 6.5 ph methinks. I feel like my sand dissolves over time, but I don't have proof. If you have water constantly flowing thru gravel I wonder whether it keeps the ph from ever dropping low enough to dissolve the rock.
I used to use reverse gravel systems in freshwater tanks, but we used a good old mj1200 pointing down - way better than bubble stones and air pumps. We used this because it seems that the angel fish fry would get sucked into the grave if set up the normal way. It also reduced the current in the tank. In such systems we didn't have any creatures growing in the fresh water gravel rocks - well not like salt water tanks anyway. As a result, it got really gunky down there.
The pessimist in me thinks that we got alway from undergravel filters because there was more money in bioballs, hob filters (the most expensive pieces of plastic ever - don't forget replacement carbon filters), and canister filters.