The (main?) active ingredient in Patio Magic is benzalkonium chloride. Patio Magic 'concentrate' is, IIRC, 7.5% and you dilute it 4:1 (or 9:1 for light growth).
My front yard is north facing and in a poor state so it needs doing every year, so I bought 5L of 50% benzalkonium chloride which will last a long time