what is the difference between ‘liquid soft ground’ and ‘liquid hard ground’?

I am etching a plate and I intend to use some ‘liquid soft ground’ to cover up my mistakes so they don’t etch in the acid in my printmaking class. In my printmaking class they used liquid hardground but I only have liquid softground at home…Will this work to keep those areas from being etched in the acid (I am using 2 parts water to one part nitric)?