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[APD] RE: CO2 and BGA

On Mon, 8 Nov 2004 07:17:34 -0500, Bill D <billinet at comcast_net> wrote:

Tom said:

"You might slap your head. What do plants do during the daylight? Remove
CO2=> Causes the pH to shoot upwards. Measure the pH on a fully planted non
CO2 tank."

Thanks for your advice. It is always useful and thought provoking. But in
the hypothesized case - essentially a soil substrate, 2 wpg, new tank,
plants not growing much if at all - I suspect that there wouldn't be much
variation in the average of the
diurnal CO2 concentrations for the first weeks. Later, sure.

I also suspect that the change in the day-to-night CO2 concentrations would
be small in such a tank compared to a high tech environment, since the
plants would be growing at a much slower rate.

So in this case, control of water column nutrients and a dose of patience
would be the only way to treat the algae problem in this case, I would


Your argument sounds very unconvincing to me. First of all, if the plants aren't growing, you WILL get algae - the plants are growing, even at 'low' light of 2wpg and no CO2 (some people will call 2wpg high light). Secondly, Tom Barr never said that their would be variations in the average of the diurnal CO2 concentrations. He just said that the pH will swing considerably over the photoperiod as CO2 is consumed. This certainly happens in nature, as described in Diana Walstad's book.
And Tom Barr has said that it DOES happen, and it IS significant, whereas you have merely said that you SUSPECT that such change would be small compared to a high tech environment. Firstly, in a high tech environment, you add CO2 to excess over the whole photoperiod, so the change doesn't matter (provided you dose enough CO2, of course...). Secondly, whether or not the change is large or small compared to a high tech tank does not matter - it only matters whether it is a significant change to the plants. Thirdly, you don't actually give any reasons why you think this change would be small anyway!

Then you conclude that control of the water column nutrients is the only way to treat algae in a low-tech tank. Why? What is your reason for believing this? There is no proper evidence to support this because as Tom Barr (please write a book dammit! or at least a paper on algae-free aquaria) has said time and time again, with the exception of NH4, you can't limit algae by limiting nutrients (at least not while you have anything else in the tank ;) ).

His argument at low growth rates is that dosing of macros is not required as fish food provides sufficient fertiliser for the plants to grow entirely from NH4 without levels becoming high enough for algae. At higher growth rates, this is not possible, and so dosing of macros is required, but nutrient limitation (again, other than NH4) never works.

Andrew McLeod
thefish at theabyssalplain_freeserve.co.uk

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