That CO2 thing does not look like it has a pressure regulator on it. Looks like a needle or metering valve connected directly to the cylinder. A pressure regulator would have a pressure gauge for working pressure and cylinder pressure or just working pressure, in addition it will have a knob to adjust the working pressure. Could be what they call a flow regulator as well. You may be able to find an inline solenoid to add to the system. It'll have to be a DIY fix. As far as ferts, yes you can do the step system and work in the nitrate later. Seems I already answered the question somewhere before.