Chuck's site is like 10 years old.
He had some speculation, however, he nor others bothered to test it. I did, folks since added it and found little issue as claimed on the site.

There are plenty of things written on the web that are outdated
Looking back, I am surprised that I got as much as I did right.

Adding more GH booster will not hinder anything and plays no negative role I am aware of or could ever show. Other's report the same that have nice reference tanks doing well.

You can analyze and isolate the Ca and Mg, but it's not likely you are short on Ca, so adding some Mg is about you'd like need to do. If the Gh was like 3 or less, then perhaps.

More trouble than it's worth for most folks.

K+ will come from the KNO3, you have plenty relative to N with KNO3, about a 4:1 ratio of K to N as far as plant demand.

So adding more is not going to hurt nor help.
GH booster is about 40% K2SO4 anyway.

Regards,
Tom Barr