using a T or a Y is inefficient. all of the air is going to be sucked in thru the side without the carbon filter because it is the path of least resistance. this means that very little air will be sucked thru the carbon.
passive intake = just a hole, no fan. you don't need fans at the bottom of...
most carbon filters aren't in-line.
single fan setup
filter --> duct --> cooltube --> duct --> fan --> outside
2 fan setup
filter --> duct --> fan -->
duct --> cooltube --> duct --> fan -->
you can use a Y as suggester earlier but it takes more air to pull thru the carbon than the cooltube...
i use a similar type product on my aquarium which has 1/2inch glass and the magnet required for a good scrub is much larger 2"x3". if you move too fast the inner magnet falls off. i think ill keep cleaning my bong with alcohol and salt
bc i tried to catch you in the chat but was high and slow!
looks nice, can you get the scrubber up high and over the lights so its pulling warm air out at the same time shortening the length of duct?