Topping off a saltwater tank?

Question

I've been told once the saltwater tank evaporates, that the water leaves but the salt stays.. Im going to measure the salidity of the tank..Can I just top it off with sink water? If so what chemicals can I use to treat the water before putting it in?

Answer 1

DO NOT TOP OFF WITH SALTWATER.
Top off the tank with freshwater ONLY.
You are correct that salt does NOT evaporate.
As the water evaporates from your tank, the Salinity in your tank WILL rise, when you top off with freshwater, the salinity will go back to it's original state.
Most tap water contains minerals, heavy metals... that are not very good for saltwater tanks.
RO-DI water is the safest to use unless you can buy TRIPPLE DISTILLED WATER.
You can buy chemicals to get rid of SOME crap from your tap water but in the long run it would be cheeper to buy ro-di water than to purchase that many chemicals.

Answer 2

PeeTee is correct and no the salt does not leave the tank when water evaporates. The only time salt leaves is when you do a water change. This is the case with both fresh and salt water tanks. As long as you are topping off before your water change you can avoid ending up with too much salt. Don't forget to always test.

Answer 3

The answer depends on what kind of water you have at the tap. The safest topping up water is totally mineral free,with a neutral pH. Distilled water or R/O water is the best. The tank should be topped up before doing a water change to maintain a stable pH and salinity. Then, the replacement water should be matched to the tank before adding it.
Changing freshwater into sea water is a complex problem.