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Placement of the external CO2 reactor

Placement of the CO2 reactor is generally one of the important
main questions.

Folks tend to have a few main areas they prefer.
In line- very popular with canister filter people and general
"reductionist". Less/fewer pumps running the system/less
electrical clutter. Good idea generally.

A)Before the filter placement. This method was popularized by
Ghori G. It often increases the amount of total water flow
through the filter versus the after the canister filter
placement. Generally, adding the reactor after the filter drops
the flow rate of the filter down considerably.
Is it easier to suck a gas bubble or pull one out of a
Water/gas leaks are less likely since there is much less
pressure on the tube and the inlet(making it MUCH better for a
DIY CO2 set up). The other thing an aquarist can do is place the
CO2 input at either the reactor tube itself OR the intake for
the siphon tube. This prevents any backflow into the CO2 system
gas lines and solves the need for a CO2 input into the PVC
reactor tube. No bubble noises into the filter for those using
their filters as reactors.

The dissolution rate of each method is not significantly
different. Most properly set up methods will dissolve 100%
either way.

Some fret over the CO2 going into their filters, this is not
much different than tank water which is hopefully not that
different from the water going through the filter(there may be
some differences depending on the system). 
In any event, the dissolved O2 levels are the primary thing for
filter bacteria(these same bacteria give off CO2 as well).
We generally use filter bacteria as backups for the plants
anyhow. If they are adversely affected, it seems to be only
minor IME/IMO.

Most Reactors use bioballs. These are specifically designed to
maintain long term flow activity without becoming fouled up with
detritus/mulm etc.
They are a good item to put before a filter and a little shake
once a week/month etc after the water change will loosen up any
flow reducing muck. No need to remove the tube.

B) Post filter reactor placement: Many folks have done this
method and there are water flow losses associated with this
method. One issue with this method is the CO2 gas inlet. It's
always under a positive pressure from the line. In the post
filter reactor, the potential for leaking is greater and for
backflow in the CO2 equipment etc. This can be addressed by
adding a check valve but these can fail as well. Alos the flow
reduction is more. These are two important considerations.

C) Independent powerhead driven reactors. 
These are flexible for most any system. These rely on the
powerhead to push water through the chamber. While adding an
extra pump, this also adds extra flow rate when you need it,
when the lights are on and the CO2 needs well mixed.

The powerhead can be used on the same timer as the lights. This
prevents plant materials from clogging the reactor/the powerhead
since it allows the detritus to float/sink off the powerhead
basket. These powerheads use little electric, cheap and small.
The timer method also reduces the electric/extends the life of
the pump.

Solenoids can be added the in line methods, but they are
generally expensive(40-80$) but for a whole sustem of several
tanks, this may be worth it for the semi automatic control(not
full pH controller control which would require independent
solenoids for each tank and pH controllers..$$$$).
The main issue is getting CO2 to the plants when they need it. 
Having CO2 added at night is not needed. If you keep several CO2
plant tanks, this might save you a fair amount of gas to warrant
the solenoid. Like check valves, these can and do fail,often
sticking open.

D)Sump placement
Folks tend to like sumps for all the monkeying around you can do
and additions that are kept out of the tank. They are good for
larger tanks and become more cost effective. Some folks want
dosing pumps/pH controllers, Reactors etc all in the sump.

Bag gravity filters can be added pre or post wet/dry sections or
added and completely remove the wet/dry tower(similar to the
Berlin SW set ups). Generally folks have a tough time figuring
out and setting up a sump but once set up, they require
less/easier cleaning, have a prefilter, maintain the water level
in the tank, allow for better replacement top off water for

Outflow from the sump reactors should feed about an 1" away from
the suction side of the return pump.    

This should give some folks a good background on external CO2
reactor placement options. 

The in line before filter works well on small canister
systems/tanks especially.
The PVC reactor tubes are easy to make and require no CO2
hole(reducing construction leaks/potentials) and makes it easier
to make. 

See Ghori's site for an example. 
Too lazy to make one? Need a big one? Email me or Shireen. I
have a few left but most folks can make one themselves.

Hope this helps
Tom Barr





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