We use high quality Humidifiers with 3 psi pressure relief valves (for safety).  Low pressure is VITAL for safety when working with a hydrogen:oxygen mixture.
Some people like to add an ADDITIONAL Humidifier to their AquaCure, to be redundantly sure that no lye is getting into their water or gas.
In that case you’d buy an extra Humidifier, a Humidifier Bracket and the Humidifier Connection Hose to have everything you’d need to add an extra Humidifier in series.