Well if you are at 7 weeks of flower then you are about 10 day's away from cutting them anyway give or take a few. No point in adding CalMag anyway there is no time for the plant to recover if there is a problem anyway.

Good luck dude....Just know if you use RO water then you need to have CalMag Plus to put back nutrients removed from the water by the RO process. It's not a bad thing to use CalMag plus with RO water anyway.