well id be inclined to listen to jen about the meds cause she knows about them, but if it were my fish I'd just add more caves, heater guard in your case and salt. maybe 1table spoon per 10L?
I don't really do ratios I just put some in, although my tank is currently salt free.
you just use normal rock salt.
furan is good to have on hand any how, and it certainly won't hurt adding it to the tank as it will keep bacterial infections at bay.