I bought RO/DI water from my lfs store And when I made my saltwater I put to much salt and my salt level is to high my lfs store is closed so I can't go buy more ro water from them can I use polar spring water in exchange for the ro/di water from the lfs store ?
Hydrometers are very inaccurate, you need a refractometer. Your LFS is probably right, I used hydrometer when I first started because I didn't know better. Found out one was off .004, the other was off .006.
Refractometer is the way to go. This is the one I have. Vital Sine Refractometer Vital Sine Refractometer
By no means do you have to get one this expensive but i think you should be look'n to spend no less than $45 to $50 to get a decent one that will last. Hydrometers can be off by alot. And distilled is the way to go in an emergency, I have three 5 gallon water cooler jug's full and on standby for emergencies. Good luck