2 tablespoons per 10g tanks with
EVERY water change is too much, and salt will build up over time. Salt does not evaporate out, it must be removed in the water. If you use salt, (I do also in my FW tanks for health and gill function, I like it).
Recommendation, if you want to use FW salt, and want to reduce the buildup that you have currently....
#1) Do not add it for about 3 - 4 water changes.
#2) To reduce any salt creep you have, if you have a lot of "bubbles" (ie.. from a decoration or airstone), move it to the center of the tank, reduce the bubbles, etc. Usually salt creep happens with a lot of spray, esp from tiny bubbles. I have a SW tank, and when I increased the flow, and got rid of my airstone that elliminated the salt creep all together.
For my FW tanks, when the salt is dosed correctly, and not allowed to build up in concentration in the water, you should have scant to no salt creep at all. You could also be getting a scale buildup from minerals in the water(hard to remove whitish dry stuff).. also.. vinegar is good to clean it with. For salt creep, I always use just tap water, comes off easily, unless there is mineral scale buildup along with it. The two get confused to some.
#3) When you begin adding salt again, only dose it for the 10g amount, once a month. Basing this on a 25% Water change weekly.
These things should help you solve your problem.
Have a great day!
nrstype