I asked this question in the general forum, but I'm still a bit confused. I'm very new to the whole DIY CO2 set up, so please be patient with me! Right now I have two bottles set up on a 30 gallon tank using a wooden airstone. My pH has dropped a bit, but I think I could get it to drop more with a more efficient diffusion method. I just got a glass diffuser in the mail and I have a brand new Eheim 2217 filter that I am setting up this weekend. I have heard that I should put the diffusor in/near the filter intake but I'm not clear on what that means. Do I just put them next to each other? Or does the CO2 go inside or below the hose?