Lazy CO2 injection


Newly Registered
1 Jan 2010
Hi Guys

Muppet-type question, but is there anything wrong with punching a hole in the inlet tube to my external filter and sticking the pressurised CO2 airline directly in and letting the filter do the mixing? I don't fancy having anything diffusing in the tank itself (laziness wrt cleaning) or having an in-line reactor (laziness wrt construction) and was just wondering if there is something blindingly obvious stopping me doing this?

Ta! :thumbup:


17 Apr 2008
The BIG End, South Wales
Apparently co2 will slowly break down your filters seals, but the biggest issue I find personally is the co2 levels become inconsistent, leading to algae problems. This is down to co2 building up in the filter, then in some cases being released in one go as a big bubble or bubbles. It really can depend on your filter and media though (sponge pads do not help at all).


Newly Registered
18 Feb 2010
I am running a nano planted tank with a very small external filter, with DIY CO2. i have experimented with several methods and have found this to be the best "in-line reactor": -

By connecting a tiny air tube (2mm diameter) about 40mm from the end of the outflow, and directing the outflow pipe to near vertical, the downwards flow is sufficient enough to ensure consistant micro air bubbles. also there is enough turbulance to keep the bubbles suppended at depth before surfacing, ensuring maximum contact time.

i did experiment with the CO2 tube entering at the outflow of the external filter however there seemed to be too much positive pressure from the pump at this point - hence moving it to the end of the outflow pipe!

the result - minimum equipment in the nano tank and excellent CO2 absorption!