Yup.. you're right, similar to what is stated on the label
"Shake or stir, then let settle for 10-20 mins. Simply decant the clear water for top off water....."
So far did not encounter content hardening before
Don't think it is used in CR.
It is mixed with top up water, but you only draw water on the top. Similar to dosing kalk.
IMO, You can use back all the media which you've used for FW tank
Please note, you still need to go through the cycling process because the bacteria in FW and marine is different.
Just like we've discussed before. Should we run the CR only during light-on period? I run mine 24hrs, and my pH difference is about 0.3 to 0.4.
You should be able to control the pH of your water using the controller.