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Re: CO2

> Won't Tom's reactor work (other things being equal) hooked up to the
> output of an existing filter pump rather than adding another pump to a
> tank?  You missing the action of the pump impeller on the CO2 but the
> co2 could be fully absorbed without the impeller.

Yes. It would be not as efficient but it would not reduce it greatly either.
You would need a check valve then to prevent back flow into your CO2 system
then also. A tiny hole drilled into your return line can be tightly fitted
with rigid airline tubing as CO2 inflow prior to the the reactor tube. If
gas flow stops then the water pressure will back flow into the gas line
unless you have a check valve. Also, Filters can get clogged and slow flows
down. I don't like the eggs all in one basket. At least with the pump,
there's some more water movement which will help get nutrients across the
boundary layer when you need it (when the lights are on and the plants are
taking in CO2). The added water current helps break up the boundary layer
allowing more CO2 gas to make it to the leaves faster and more effectively.
Disc do not do this unless used in conjunction with a pump and cannot be
used well in shallow sumps.
    Another issue is if your pushing larger volumes of water through the
reactor some of the gas could potentially by pass the unit. The in/out pipe
diameters are 1/2inch. It would work on small canister filters well or if
you used a splitter and a valve to direct only a portion of the water to the
unit(say 100-200 GPH or so).
    Check valves and solenoids just do not instill the greatest confidence
for myself. Bad past experiences.
If someone wants a modified reactor for a canister filter, a CO2 input can
be drilled into the tube for injection by that method if they wish. I will
not recommend it personally although it will work with a check valve. They
will also need to keep the flow rate in the 100-200GPH range also and place
near the top of the tank to help minimize backflow pressure.
    The reason I use a pump is that it is replaceable, cheap, uses all of 3
watts/hr(less than many solenoids) creates positive suction flow(why do you
need a check valve if something is always pulling rather than back
pressuring?) you can use it with DIY unlike pressure set ups, it's simpler
to set up(just fit the tubing together and set on the tank, add CO2
line-bubble rate turn on pump), one less thing to buy, actively moves water
even more during the photocycle allowing faster transfer of CO2 gas to the
plant's leaves, flow rates stay the same compared to filters which as
designed to clogged up to some degree and having a dedicated pump for the
all important CO2 part of our hobby. At least if your filter goes kaput,
your CO2 will still be fine(and some water movement). And conversely if your
CO2 goes kaput your filter will still do fine. Either way the fish win at
But having a pump provided allows any system set up or CO2 source to be able
to use unlike other external CO2 systems. I'm also about 1/2 the cost and
you get a pump with that. DIY folks will save the cost of the unit pretty
fast on fewer bottle changes and bottles needed and when they upgrade to
canned CO2 they can use the same reactor.
Now consider what happens when your check valve or solenoid goes kaput or
your canister? 
I *see* what your saying and what folks would like to do here with this
issue. Sumps are great for getting stuff out of your tank IMO if that's your
goal. A small Rio 180 is pretty easily hid in a tank. Glue some cork to it
and attach Bolbitis, Java fern etc to it if it bugs you. A suspended fern
near the surface won't look bad and the pump is about as small as they can
make them. I would recommend this for anyone using internal reactors to hide
them better from the front view at least.
    If you have a canister , you can buy the reactor without the pump also
and I can add a rigid line into your tubing or directly into the unit. If
you have a pump and need no other modifications, I also will sell the tube
only for a reduced price(-5$) if you have your own pump. The max size for
the unit is around 150-200 gallon but I'd rather get something larger for
folks with tanks that size and will make a 2 1/2 diameter unit with a larger
pump so they can get good response times and good mixing within the tank.
I can make sump style model that really works very well much like the big 4
foot model also but these are for larger tanks. Even CO2 distribution is
important and over sizing things is better than under sizing IMO.
Tom Barr  
> Scott H.