You really shouldn't "medicate" in the main tank anyway... Remove sick fish and place in a QT/Hospital tank to treat.
1.Most Meds will affect the LR/Biological filtration.
2.Other fish in tank may not be Ill and excess Meds could adversely affect them.
3.By moving to a "smaller" QT Less Meds are needed(cost) and it is easier to figure dosage..ie:10gal QT @1 tab per 10 gal or 55gal display with 45lbs LR do I have 30 or 40 gallons of water in there?
4. Removing fish for ICH/Hypo treatment allows "fish borne' parasites to die off in main display.
But, LR/LS in a "healthy" display will NOT harm fish, quite the opposite...It is beneficial for the overall quality of life for your inhabitants.