I mean, it's important that it is within some range but good quality freshly mixed salt water should be fine. I've never heard of anyone having to actively intervene to change their hospital or QT tanks pH. Make sure you tank is well aerated I guess, usually this is accomplished incidentally by a powerfilter that also provides a place for the biomaterials. For marine fish nitrate and nitrite are irrelevant under reasonable circumstances. If you lose a fish from water parameters, it's going to be from ammonia, temperature or salinity. The last two are easy barring human or mechanical failure.
