I agree with rfeiller.
Can you pre-treat all your new water (adjust ph,treat for chlorine/chloromines, match the water tempt ) before adding ? Maybe you could at least do a 50% water change, a day or two apart.
I'd add salt now, and as you you change the water. Sea salt is good. However, it may cost a little more.

I gave the correct ratio...1 kg:1000 L of water...or.. 1 gram:1 liter of water...(dang metric fish pooh, who decided to measure with 'tens'... )
UF is right, I wrote PPM, it should be PPT..... 'parts per thousand'