when the water goes down thru a small tube to a larger tube the speed at which the water travels slows down alot, as well as the volume of water per sq inch
a 2 inch reactor pipe can slow it down about 30 times the speed at which it is flowing thru the eheim pipe
there will not be enough flow to discharge the air in the reactor
you will get a air gap at top of reactor that will slow diffusion to a crawl
on the top of the reactor or top of bend coming from tank you need a t fitting with a valve you can open so the air pocket has a place to go out of the reactor chamber
once the air is bleed shut valve then your fine
i make mine with a t going to valve that has a hose barb on it that i attach temporarily to a small hose
this way its easy to bleed the line at first or if there is a build up of non co2 gasses over time
and if any water comes out it will go thru hose to a temporary bucket or other container
if your tank is drilled its not a problem because if you stop the filter the air goes straight out the top
into tank
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You're gonna have to clarify that a bit more. What trapped air would you be talking about?