i allways had trouble using ceramic glass diffusers with DIY co2.
It takes so much pressure to push air thru the ceramic disk that I had terrible leaks every where.
So if you just poked a hole and pushed the air line into a plastic bottle I bet you may have the same thing going on. I finally fixed mine by using a screw in fitting that I got at a auto parts store. 1/8" npt male to 1/8" barb was the name/style.
5 per minute does sound low but DIY starts out slow for a few days ,and ramps up over the next week or so. It hits its maximum output and stays there for a week or so and then starts ramping down. Sort of like a wave of co2.