3 In 1 Diffuser Won't Go Past 3bps

Is anyone familiar with this kind of diffuser?

https://www.amazon.com/ISTA-Compact-Diffuser-Counter-Aquarium/dp/B00S5A77HQ

I bought this when I went to Taiwan. One of the lfs I went to had one (but the bigger version) in their tank, and I really liked it, so I bought the smaller one. But even if I have the co2 tank and the regulator valves all the way open, it doesn't go past about 3bps. And I'm somewhat reluctant to do that since I don't know if pressure will build up somewhere... I have another diffuser (not 3-in-1) that doesn't make as fine bubbles, but the co2 comes out of it just fine, so I don't think it's a problem with the rest of the set up. Any ideas on what's wrong with it or how I might be able to fix it??