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Is there any benefit to having a solenoid that maintains the Co2 at 30ppm throughout the day? My Co2 naturally decreases to 15ppm from the plants using Co2 by the end of the day. Does this mean that they loose momentum as the Co2 decreases?
 

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I think its best to maintain a constant co2. Do you have algae problems? If not and you like the plant growth i guess dont mess with it.
 

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on and off?

You might want to turn the CO2 up during the day and off at night.

Your plants are consuming the CO2 faster than you are putting it in, but running at a high rate all night might be dangerous.

It is a tough thing to predict, for you have the known input rate plus fish input, minus the plants and losses during the day, then the plant intput at night plus the fish minus the losses during the night. Too many unknowns to solve that equation! You just have to measure and test to see if it works better.
 

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Generaly speaking, I have seen better results with 24/7 CO2 supplementation than with controler CO2 supplementation. A few people in sfbaaps have tried controler CO2 supplementation and encountered technical problems. When they reverted to 24/7 CO2 supplementation they often had less problems and greater success.

I think the key factor to consider is reactor efficiency. Controler CO2 supplementation needs a reactor that can change pH very quickly. If the reactor is too small the controler seems worthless. That said, if a controler or probe goes bad they can poison a tank with excessive CO2 when the reactor is sized correctly.

Many aquatic plants are well adapted to changing CO2 concentrations. I have yet to hear of a plant that requires controler CO2 supplementation. It is not uncommon for a tank to have a pH swing of 6.4 - 7.4 if it has an undersized reactor and lots of light. Your plants will do fine with a swing of 10 - 30 ppm CO2 each day because they can take in C faster than they can use it if light is sufficient. When they accumulate excess they release it during the night phase.

This ability of plants to absorb more C than they can use makes large pH swings an indicator of possible nutrient limitations. They give off excess C as CO2 during the night and magnify your steady rate suplementation. I think P limited conditions have produced this effect in my tank. When this happened I observed a unique combination of, lots of pearling, a large pH swing, and very slow growth. Look here, for Rodger Miller's explanation and lots of links to more informed biochemistry sources:http://www.aquaticplantcentral.com/forum/viewtopic.php?t=1290

My current practice targets steady healthy growth with moderate pearling and has a pH swing of 6.6 - 6.8 with 24/7 CO2 supplementation. Sorry, I don't measure dKH but you are welcome to come over and measure mine if you need to know.
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Jeff
 

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A little off topic, but this explains a lot about my tank.

Decent pearling, slow growth, stunting, and pH/KH inconsistencies despite daylong injection and almost 52ppm N weekly (5.5 wpg).

This makes me wonder, if limiting P produces slower but still decently healthy growth (which it has in some species in my tank), might one want to limit it to decrease momentum but maintain health, say in a vacation/photography situation?

Just a thought.
 

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Why not less light then, rather than less PO4? Since slowing the growth rate down to allow more time and more stability is the goal then?
PO4 will work to slow things down but so will less light.

Algae is not limited by low PO4, but it IS limited when there's less lighting to a much larger degree than submersed plants.

Regards,
Tom Barr
 

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plantbrain said:
Why not less light then, rather than less PO4?
I suppose that would work fine but that isn't my point here. Regardless of the light level chosen one can use P availability to regulate desired growth rates and plant appearance. This doesn't neccesarily mean running P down to limited levels is a goal. Rather one uses P to regulate N/P ratios in order to achieve particular goals of appearance or growth rate.

In the instance of this thread, extreme P limitation is mentioned as a possible cause of large pH swings. In doing so, I suggest that more factors than pH, dKH and dissolution rates might be considered when one examines their daily plant respiration clues.
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Jeff
 
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