Discus can be raised (but not bred) in hard tap water but the water must be kept pristine by doing daily water change, warm, and avoid substrate or mixing with other species to minimize bacterial count. Discus are so weak that short of providing those ideal conditions, they are vulnerable to HITH and a range of other infectious diseases, You don't see holes easily in discus because their head is small and under less than ideal conditions, they will never reach full size to become visible.
If you can provide the same ideal conditions for your Geos as discus, they will likely thrive in your hard tap water. What I am trying to say is that treating your Geos with mediation but not changing the fundamentals that caused the HITH is not likely to be effective.