Your going to eventually turn that tank into a sw tank.
If Mturner615 keeps dosing like he is, with every partial water change, then yes, that could happen in the long run. The most common misconception, is that people tend to dose say, a 10g amount for a 10g tank. When in reality, there may be only 8.5 -9 gallons of actual water in the tank do to displacement of the gravel, decor and other items. Couple that with some beginners not knowing that the salt never leaves, it has to be manually removed (ie.. taken out with water changes), and if they redose the salt, it is common for people to put yet another "10g worth" of the Salt dose, instead of the say only the 2 -3 gallons they removed.
BUT...No... you WON'T turn a FW tank into a SW tank by using FW salt, dosed properly, and following proper water changes and aquarium maintenance. I use FW Salt for YEARS in my FW, non~planted tanks. I buy the salt made for FW use, not marine or sea/reef salt. I also maintain a reef aquarium, so I do understand the difference, and the potential for disaster.
Personally, I use salt for several reasons..
*Some Disease prevention.
*It assists in healing.
*Promotes formation of slime coating.
*Improves gill function
*Reduces the uptake of nitrite, If nitrite levels are an issue.
*It can be effective against some parasites.
Mollies, for instance, do better with some salt added to their environment.
When DON'T I use FW salt. I do not use it in my PLANTED TANKS, Tanks with scaleless fish (loaches etc.)
The addition of some FW salt can be beneficial, when used properly (Stress stress stressing this).
FW Salt is also one of the best remedies to use as a treatment option for several disease and parasite issues, but it must be done outside the main tank, in a separate or "hospital" tank.
I understand the rationale for using FW salt, it is the subject of controversy, because there are pros and cons for and against. There are as many people who use it, and those who think it is all bunk. However, sodium is an important element living things use for cellular & fluid activity. I, as you can see, am in the "FOR" catagory, but with close monitoring and dosing that it requires.
Here is a nice site that simply explains some of them.
HERE