Nitrate of 20-40 ppm may be too high for some Geo's, some species can be intolerant of such a high level.
Most of their natural water have nitrate under 5 ppm (if not 0), and the seasonal natural tannins, are also antibacterial.
If it were me, I'd increase my water change, and filter cleaning schedule to bring nitrate down to 10ppm or under.
And depending on how the breeder raised them, even 7.4 pH may be slightly high, depending on conductivity (mineral content), if the breeder used RO to bring conductivity down, and yours is high, it could be a problem.
You may wonder why only the Geo's are affected, and not the others.
P-bass seem to have a much higher tolerance for water with high mineral content, here in Panama they thrive in lake Gatun where pH often rises to 9 and the lake gets surges of sea water (although they don't get to the sizes found in the soft waters of the Amazon).