For those white stains this is what I did. Get a bucket of water and add a cap or two of bleach. Wash the inside of the tank and do a really good job. Rinse the tank off really good. Then let the tank air dry for a day or two. Any bleach will be gone once the tank drys out. Then add your SW
and it`s not necessary but if it makes you feel better then run some dechlorinator in the water. This is what I`ve done several times in my new SW
tanks when I first got them. Another thing you can do is wash with a White vinegar/water solution. I`ve heard from others that this will work also. But do remember that if you use bleach you must let the tank air dry completely. This is important.