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Re: CO2

> [[ I can think of only one situation:  the reactor pump goes out of
> service and the CO2 tank is empty and cools enough draw a vacumm on the
> line.  A winter storm that knocks the power out could do this, if it
> did so when your CO2 tank was empty.  Pretty low probability there. ]]

I've never had it happen. The tank would have to cool fast and be empty.
Unless you live where it gets cold fast and don't heat your house
etc.........I've had my tanks go empty and number of times. Never seen any
evidence of backflow. Been running things like this for many year on many
tanks. Never seen any evidence of backflows. Believe me, I have used DIY for
many moons, I know backflow and related problems. Those things react much
faster and to a greater extent than Gas systems.
I what will fail first? A solenoid or a check valve? Or a backflow in this
type of set up? I'll let you decide. A simple gas line loop will solve a
small amount of backflow or if you run the gas line upwards for a few
inches. Don't check valves and solenoids actually cost money (gasp!) also? I
see no need for them in a well designed set up that uses suction. They can
be used if it makes one feel safe but I will not provide them and add the
associated extra cost for what I feel is unneeded. If you've had a CO2 dump,
solenoid stick open, check valve break, you have not experienced Murphy's
Law fully. I have not had a dump, but the other two have nailed me. It won't
happen again. Needle valves and DIY will not have CO2 dumps so I'm safe
>> 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. 
> [[  I only brought this up to discuss a potential option for one less
> thing in the tank, even though it (a small pump) is a very small thing.

That's what sumps are for.

> Just getting the reactor out of the tank is a big improvement in
> getting things out of the tank.  I was (am) just curious about going
> that way one step further.  So I really appreciate you're taking the
> time to respond in such detail.

Then get a sump:) Or do you like that heater and siphon tube in your tank? I
think it's preferable to have something up near the top rather than poking
down the whole height of your tank.

>> The max size
>> for
>> the unit is around 150-200 gallon but I'd rather get something larger
>> for
>> folks with tanks that size
> [[ Well, I actually had in mind a 150 gallon tank with a moderately
> high fish load, now that you mention it.

You _need_ a sump for a tank like that. Big display tanks are easier to
handle using a sump and over flow. Also if you've invested that much into a
tank for space, lighting etc you kind of owe it yourself to do it up right.
 A DIY'er can make a sump that will kick a canister's butt, keep the water
level the same, greatly reduce filter maintenance(those prefilters are
mighty easy to clean and fast), keep everything out of the tank, suck off
that surface scum to maximize light penetration, remove the water with the
poorest CO2 levels, constant level in the tank itself since a sump fluxes
due to evaporation but the tank level does not(but you can add an automatic
refill via a float switch or float valve or a gravity feed device) and cost
less than the canisters and large water changes don't break the siphon and
belch air bubbles afterwards. Yea there are a few minus but the benefits
outweigh them on large tanks which your spending a bunch of $ on even if you
are cheap DIY or if you realize it or not. You got a big plant tank your
going to spend a fair amount on it. Don't want to spend a lot... get a 55.
And some of these cheap folks then go out and buy Discus at top dollar:)

  And plenty of filter media
> capacity and pump output.  The larger the reactor diameter, the greater
> the surface area in the reactor, which yields higher potential
> absorbtion, right?  So it could accomodate a higher pump output,
> yes/no?

Up to a point. By pass will occur beyond 300 gph or so. Even if your firing
lots of bubbles in there. Most will still get absorbed but a little will get
lost and shot out the return.

 I usually don't like using things that are at or near their
> maximum capacity right off the bat, out of the box, so to speak -- it
> means there is no margin for error, changing conditions, reserve
> capacity, etc.  ]]

Get a 2 1/2" model. Good for about a 300gallon plant tank. Cost 10$ more.
You do not need such high flow rates to get dissolving power. You can use
the larger units of a smaller tank if you so choose. The dwell times are
longer for the water gas contact. It'd be great for a 150 gallon tank.

I'll have a few at the AGA conference for folks to look at. This is not
brain surgery:) Pretty simple devices.

Tom Barr