[jmhart]

having to refill a 5lb bottle in 3 weeks sounds like you had a big leak somewhere.

Ditto.

I run my co2 into the intake of my Eheim 2128. 100% diffusion. The first time I set it up, I had a small leak, had to refill in about 4 weeks, now I get several months.

However, now that I mention it, it's roundabout time to switch it out, and I'm out of town...here's hoping it hasn't run out.

 

[jmhart]

I have no problems at all. If you think about the flow going through the filter, most of the co2 is chopped up and diffused before it even reaches the impeller. Occasionally there is a slight build up of gas that reaches the impeller, but again, I've had no problems.