Water changes do not bring up your values, at least to that of original amount unless salt has elevated (above what you normally want to run) values.
e.g.
Fresh SW has an alk of "100", over time that number drops to "80", you do a 10% water change with the same brand of fresh SW, so 90% of the water is "80" and 10% is "100" the result after you mix the two is 0.9 x 80 + 0.1 x 100 = 82. So you barely raised your alk in this situation. Even with 25% water changes 0.75 x 80 + 0.25 x 100 = 85, barely moves the needle. Unless you do a 100% water change you'll never get back to those day 0 numbers.
Now if you use a very highly elevated mix that say mixes to "150" but you're happy with "100" then sure a 25% change 0.75 x 80 + 0.25 x 150 = 97.5, so you're at least ballpark there, but usually salt mixes will have a one or two elevated values will be "average" in others, so you might use Salt mix Y to bring up your alk, but then your calcium ends up dropping.
You really do need dose and not rely on water changes to increase your chemical stew values.