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I don't own a CarboPlus, I've never used one and I don't have an opinion
about them. Paul Sears has a theory about how they work, and I want to
propose another idea. I think they work pretty much like the electrolysis
CO2 system sold by M3, but differ in their construction. The
Marine-Monsters web site provides a good description of how the
electrolysis CO2 system works.
From descriptions I've read and pictures I've seen, it appears that the
CarboPlus submersed unit is an integrated anode-cathode pair, with a
carbon anode and probably a stainless steel cathode. It is the carbon in
the anode that supplies the carbon for the CO2 produced by the system.
The anode is eroded with use and needs to be replaced periodically.
The unit works by maintaining a voltage between the anode and cathode that
is sufficient to break down water.
The half reaction at the cathode is
4H2O + 4e- -> 4OH- + 2H2
The half reaction at the carbon anode is
2H2O + C -> CO2 + 4H+ + 4e-
Both the hydrogen and the CO2 should be produced as gas. The reaction
produces 2 molecules of hydrogen gas for each molecule of CO2 produced.
Of the visible bubbles produced, only 1/3 are CO2 bubbles. The rest are
Ideally, the 4 hydroxide ions (OH-) and the 4 hydrogen ions (H+) would
combine to form 4 water molecules. However, the two ions are not produced
in the same location, so there won't be a 100% recombination to form
water. Instead, some of the OH- will react with bicarbonate to form
carbonate. In most water that will cause a calcium carbonate crust to
form on or near the cathode. An equivalent amount of the hydrogen ion
produced must also react with bicarbonate. The effect of both reactions
is to lower the GH and the alkalinity of the water, with a larger decline
observed in the alkalinity than in the GH. The actual amount of decline
will be highly variable.
A pH probe placed at different points near the working surface of the
CarboPlus unit should show very large swings in pH. The pH variations
may be negligible as little as an inch away from the unit.
The hydrogen gas produced by the unit should have some effects of its own.
Dissolved hydrogen gas is like candy to anaerobic bacteria, so a tank with
a CarboPlus unit may support some real active anaerobic activity.
Further, the hydrogen gas probably should be picked up by an ORP meter; I
imagine that truly bizzare (low) readings are possible.
I don't know if this will help anybody get more out of their CarboPlus,
but it might help explain some of it's behavior. In particular it might
explain how you can get a nice steady stream of bubbles off the unit
without having much CO2 production. Only about 1/3 of the bubbles are
CO2. This also might explain the water-softening effect that some people
have observed. It doesn't explain why some people seem to get better
results from hard water then from soft water.