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Turning CO2 Off at Night

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</DIV><H1>Should C02 be shut off at night</H1><DIV id=Qtextbox><P><STRONG>Author: masterry</STRONG><BR><BR>Hey everyone

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I have been reading a bit and a few sites seem to suggest that you turn off c02 at night and that you cant have a air stone running during the day or it will get rid of the c02.

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Is this correct, should i turn co2 off at night and not run a air stone during the day?

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Thanks Ryan

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</P></DIV><H2>Replies »</H2><DIV id=Atextbox><P><STRONG>Author: hungsta</STRONG><BR><BR>Hi my understanding is that the airstone should not be turned on because it creates surface turbulence which is where co2 and o2 is exchanged........so best to minimise surface disturbance.....

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Regarding the other issue, you should not turn off co2 at night... because there is no harm in leaving it on (your fish will not suffocate), if you do turn it off the ph flutuations is more likely to harm your fish...

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However since plants take in o2 at night you can add in some current.

</DIV><DIV id=Atextbox><P><STRONG>Author: masterry</STRONG><BR><BR>Thanks Hungsta

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Does anyone else have an opinion to this or disagree with what hungsta said?

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Ryan

</P></DIV><DIV id=Atextbox><P><STRONG>Author: E4G13M4N</STRONG><BR><BR>My understanding is that the plant dont absorb the Co2 at night, so basically its a waste of Co2 IMO unless your using the home brew

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When using the Carbo Plus type of unit they recommend only to use with a timer in conjunction with your lights, so Co2 gas type would be the same..

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^Mark^

</P></DIV><DIV id=Atextbox><P><STRONG>Author: MagicaDiSpell</STRONG><BR><BR>Plants are net producers of oxygen only during exposure to light and net producers of CO2 at night. So, yes from that point of view it would be a "waste" of CO2, if you kept it bubbling at night.

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However... (isn't there always one?) the fluctuations in pH could be sufficient to stress your fish, damage your bacterial fauna in the filter and also stress the plants.

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Therefore, I would recommend you kept the CO2 bubbling at night also. Similarly you should also keep the airstones either running all the time or not all, fluctuations in dissolved gases will stress the fish. This is one reason for not extremely super-oxygenating your water, because if you have a power/pump failure, the fish are so used to a high oxygen level in the water, that they wont be able to cope with the lower levels. On the other hand fish that have been kept at moderate oxygen levels will be albe to cope better.

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Sorry, I digress, but the message I guess is: keep your system as stable as possible.

<P><STRONG>Author: Brett4Perth</STRONG><BR><BR>During the day plants convert CO2 to O2 with the aid of light.

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During the night plants use O2 and make CO2.

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So I guess it is not really "stable", even if the only change you make is to turn the light on and off.

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In practice I don't think it makes all that much difference. My heavily planted tanks have CO2 running all the time and the fish don't seem to suffer, but they are relatively lightly stocked. Theoretically, if you have a heavily planted tank and high fish load, then the fish could run out of O2 at night. This is because the plants are using some of the O2, not due to the CO2 content of the water. Turning off the CO2 doesn't help this, aeriating the water at night does. Never seen it happen!!

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Brett

</P></DIV><DIV id=Atextbox><P><STRONG>Author: PHL0703</STRONG><BR><BR>I think this has been hotly debated for some time, but the final consensus was the the pH swing was more harmful than anything else. Anyway, top get some results...

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Some aquarist in the US measured the O2 saturation levels (which is what is important to the fish, not so much the CO2 level unless it's very high), and it was 108% daytime, and 96% just before the lights came on in the morning. So there is no problems for fish. pH swing was from 6.8 to 6.6, so no problems either. Can't remember the CO2 level, but it wasn't significant, as some will be lost ayway through the surface.

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When CO2 was turned off, the O2 levels were not significantly different, but now the pH was 6.8 to 6.7 to 7.2 in the first half hour of the light coming on, before falling back to 6.8; the pH swing was caused by the plants using up the little available CO2 before the reactor could dissolve more CO2, and although it doesn't cause fish death, it might.

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So it's probably better to leave the CO2 on all the time, keep it in the 20-30ppm range daytime, and leave it. At least that's what I've been doing.

</P></DIV><DIV id=Atextbox><P><STRONG>Author: c2105208</STRONG><BR><BR>Firstly, CO2 and O2 levels dissolved in water are independant. That is, if you have high CO2 levels the dissolved oxygen will not be affected and vice versa. CO2 is more affected than oxygen by surface turbulence (presumably due to being a larger molecule).

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CO2 stays on at night - Reason being for pH fluctuations. Basically the water will reach a stage where it's not likely to keep any more co2 in the system anyway due to the exchange rate between the surface and the environment surrounding the tank - it will reach an equilibrium. Unless your co2 system makes like a fire extinguisher in the tank and your carbonate hardness is scarily low, you will *not* see pH fall to such a level as your fish will *ever* be harmed if they are suitable for planted tanks. The process of co2 interchange between the water and the air is somewhat between diffusion and advection... the diffusive component is governed by ficks equation which states that the rate of exchange is proportional to the concentration difference between the two media - i.e. when the concentration difference between water and air is at such a rate that the rate of interchange is the same as the rate that you're pumping in CO2. This is also governed by the diffusivity of co2 in air and water and gets compliated but just trust me the fish will be ok under 'normal' co2 induction rates

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If CO2 is turned off at night, all that will be done is that co2 will be lost from the system and none coming in. This creates net imbalance in the morning when lights come back on and co2 comes back on - very low co2 present not good for your plants, and means a large pH fluctuation has occured (a rise in pH overnight) between when the lights were turned off at night and when the lights came back on. True, plants respire in dark periods, but the rate you will lose co2 from the surface is far greater than the rate of co2 production in the plants through respiration.

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In short, leave the CO2 on over night. No the plants aren't using it, but it keeps a better system equilibrium for the reasons above (plus more complicated ones I wont go into).

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Regarding airstones - yes leave the airstones off. In general, you dont tend to see airstones in densely planted tanks at all - either night or day - due to co2 loss. So I would say if you *HAVE* to use an airstone use it at night, otherwise dont bother - the plants should produce enough oxygen and there should be enough surface area available on your tank to sustain what fish you have in there. Additionally, you dont tend to see many fish in a densely planted tank for this reason - the focus is then on the plants not so much the fish. Less fish = less need to worry too much about dissolved oxygen and airstones etc.

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Hope this helps,

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Cheers,

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Adam

</P></DIV><DIV id=Atextbox><P><STRONG>Author: b3dlam</STRONG><BR><BR>I would agree with Adam.

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If the tank isn't densely planted, having the co2 on at night will not be a problem. Unless it is heavily planted and heavily stocked with fish, then an airstone (on a timer) at night will help.

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