This is just one routine, it's not written in stone.
You can use less in many cases, you can dose 2x a week in some cases, some dose daily, some do water changes over long time frame, say once every 2 weeks, some do smaller water changes(the trade off is more possible build up/more deficiency potentially), some larger(better stability to the pre set dosings).
Adding K2SO4 will not hurt, but there might be some other factor involved besides K+ alone.
You can leave it, I have not used K2SO4 as a part of a routine for several years now, few would say my plants/tanks have K+ related issues in any way.
But I think it's unlikely the low K+ had any nbearing unless there was not enough KNO3 being added.