Lifespan? Its soil. Keep it closed from bugs and should be good for yrs. May need to be moistened occasionally but im not fully understanding your question. People recycle it for several runs so in a bag….
I use F.F. Ocean Forest & perlite/vermiculite mix.Hot is right,out of the bag it has 550ppm so I don't add nutes for one month.I have made and mixed my own soils for years-until finding F.F. Ocean Forest.Only thing I add is a tablespoon of Epsom salts every 5 gallon and always perlite/vermiculite mix.