Here are some pics I took of my 8 gal when I changed out a noisy fan: pics:

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The tape closes the space between the hood/reflector and the fan. This forces the fan to only move air from where it's supposed to.

,PAY ATTENTION!! Keep track of where the fans plug in!!

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,My hood tapers to the side so I made sure the tape does to. Be sure you watch the orientation of the fans. One of mine pulls air into the hood and one pulls air out of the hood.

,I'm pointing to the posts the fans mount to. Make sure that the tape is around the mounts, it will want to get in between the mount an the fan.

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I hope this helps you. The only other issue I've had is low
PH due to poor gas exchange caused by the hood. I have an airstone in the third chamber which draws in air from outside the house. My
PH went from 8.0 or so to over 8.25 after this mod.
There are a couple other mods I've done, if you want to try them let me know.