OK -- so this path forward will be entirely up to you.
Your salinity testing has shown, using different methods, that your salinity is around 900 ppm. Correct?
If so, add 2000 ppm worth of salt. Let it circulate really well -- have the SWCG powered OFF during the salt addition. Brush, do whatever to mix it in. Then test it. If around 3000 ppm, start the SWCG.
Warning - if you end up with too much salt, you will have to drain the pool. I am only suggesting this based on the data you have provided.
Your SWCG should not get calcium buildup quickly if your chemistry is close to correct. My caveat to that is if the SWCG is failing.