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Re: CO2 reactors

Roxanne wrote:

> Question is:  Given this increase in efficiency, what more could I expect
> from a unit either inside or outside the aquarium designed to mix CO2  such
> as the Hydrologix, Tom's incredible unit sold by SDP's, or the Mixer J sold
> by M3?
> Is it worth the expense to go further?
> Perhaps the CO2 damages the bacterial cultures in the filter with the
> increased acidity?


The pump in an Eheim filter (at least in the one I recently bought) is
at the top of the canister, so any CO2 bubbles that get through the
media can hit the pump impeller, making a noise.  If it accumulates
somewhere before it hits the pump then it can create a burp.

Whether or not you see bad behavior depends on details of your setup. 
If you don't get popping or burping from the impeller then it's probably
working at 100% efficiency and you can't get better.  If you do get
popping or burping then you might be able to prevent that by using
something that will reduce the size of the bubble entering the canister;
your existing diffuser, maybe an airstone, or a nozzle with a small

I seem to recall that the optimum pH for nitrification is close to 8. 
In a tank with a pH at or below 7 the pH is already somewhat
suppressed.  The pH inside the canister when you are feeding CO2
directly into it must be quit a bit lower than the pH in the open water
of the tank.  So I think you're right that feeding CO2 into a canister
filter could damage the bacterial culture inside the filter.  That might
take the nitrification process from supressed to barely functional. I
run most of my tanks without filtration, so I guess that prospect
doesn't bother me very much.

I've been feeding CO2 into a Magnum 350 for about a year.  The pump in a
Magnum 350 is at the bottom of the canister, so CO2 never reaches the
impeller.  At the prices you're talking about it might actually be
cost-effective to buy a Magnum 350 just to use it as a CO2 reactor.  The
Magnum is far from perfect.  Gas -- I think it's mostly air drawn
through the o-ring seal -- sometimes accumulates at the top of the
canister and that can cause some noise.  I believe there's a DIY
modification to the Magnum 350 that makes that problem pretty trivial,
but I can understand why you may not want to modify the filter.

Roger Miller