Most plants do not care what the levels are as long as the GH does not hit zero. They do need the Ca and Mg that are measured as GH.
You sure could go measure the lake where the fish were caught.
Bluegills are also found around here in several sorts of water, so I would not be surprised to find out they are quite adaptable.
If your system is working, do not make changes, just check that you are maintaining it, the conditions are stable.