Shouldn't add salt to top off. You will raise your salt level by doing that. Salt don't evaporate from the water column. The only time you may loose some is IF water splashes and the salt goes out the tank.
Ok ty my salt was going up & i was thinking this was why, not mush about 29, i pulled out my top & now adding new RO, evey thing is doing good & thinks to your all,s help i can keep it that way