Hi. I use a pressurised system, but after changing a bottle it does take some time before anything appears at the diffuser. 1 bubble every 7 seconds means only 108 bubbles or so in a couple of hours. That could take a while to build enough pressure to start diffusing. Did you blow through the diffuser line to check it out before connecting up the mix? Basically, if you can't blow through it relatively easily there's too much resistance.