Is it ok to add salt in the evening with the pump off? Will leaving salt resting on marcite for 15 hours damage the marcite? It would be more convenient if I could just dump the salt in and let it slowly disolve at it's own pace.
Salt that is dumped into pools will probably dissolve adequately without causing any visable damage to marcite finishes. However, it is known that leaving concentrated and undissolved salt on cement/marcite surfaces can be detrimental in time. I suggest brushing salt around until dissolved.
With out the pump, the salt will dissolve, but it will not mix into the bulk pool water. Instead concentrated salt brine will sit in contact with the bottom of the pool until the next time the pump is run (or a long time passes). It is best to run the pump.