what is ideal, i thought 1.025 was, but i don't trust my hydrometer, and it always says 1.021 even if i add a heavy salt mixture.
To top off simply means your water level isn't "all the way to the top". When the water from your tank evaporates it leaves the salt (salt doesn't evaporate) therefor when you want to top it off no need to mix anymore salt its just as simple as topping off with fresh water. Eventually when you really start getting into the hobby you can get an ro/di unit and hook it up to an auto-top off which does the job for youupdate: salinity is at 1.025 and im curious...it says in my book to mantain this you have to top off with freshwater...so when i do a water change i should top off the tank with freshwater first...then take out 20% then refill with salt water? i never had to worry before because my level was low...no i dont want it too high.