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Thread: Turning off CO2 at night, could someone explain this to me?

  1. #1

    Turning off CO2 at night, could someone explain this to me?

    I'm sure when you saw this title you'd think it'd be a simple answer, but I'm already aware that plants USE oxygen and give off CO2 at night, the reverse of their daytime activity.

    My question is this: If my aquarium water is naturally around 7.0-7.1, and with C02 injection is around 6.6-6.8, when it comes to night and my Co2 shuts off, won't the water pH climb back to 7.0-7.1, with surface agitation that turns on during evening hours?

    There seems to be a conflict here. Because I try NOT to have agitation during the day so the C02 will stay in the water, but at night to assist with O2 exchange, I have a powerhead that turns on. Now as I understand this is the way to go so plants and fish can get their oxygen at night and C02 can be expelled. However, logic tells me that this is a big fluctuation in pH that is happening every within every dayspan, as C02 is in the tank during day to give a unnatural pH, then leaves it during night, regaining its natural neutral pH.

    Could someone explain to me if my thought process here is correct and if this change in pH daily is okay?

  2. #2
    Join Date
    Sep 2007
    Location
    South Florida
    Posts
    5,513
    Hi,

    Yes, the ph will fluctuate.

    This is a nomal scenario in nature and in c02 enriched tanks as the 'sun' gets higher, plants wake up, optimal c02 levels are reached, etc. PH changes more than people think IMO.

    Here is a thread that spoke to ph shifts and fish health.

    http://www.barrreport.com/fish-plant...PH+fish+health


    I go from 7.3 at night to 6.6 during the day using c02 with no adverse affect on fish, inverts, plants.

    Just have your extra powerhead turn off and the c02 come on about 60-90 min before lights come on to get the c02 back in the tank again, as the level will be low after all night of 02 enrichment.

    Hope this helps.
    Last edited by Gerryd; 11-24-2007 at 07:55 AM.
    Thanks,

    Gerry.

    'When something's not right, it's wrong'. Bob Dylan

    Current 220 scape

    http://www.barrreport.com/showthread...3219-220-video

  3. If your pH is only changing from 6.6 - 7.1 it doesn't sound like you have enough co2. I could be wrong but I'm pretty sure that with a change that small there's no way you could be injecting enough co2. But if you have low light it won't matter all that much.

    Since I'm running diy, the only way for me to keep co2 levels high enough is by letting it run all night, otherwise after 12 hours of dropping it takes another 12 hours of injecting to get it up high enough again. My fish don't seem the least bit stressed, I do have quite a bit of circulation so I guess O2 levels are high enough.

    I've had lots of issues keeping co2 stable in the past, with pH fluctuations of 1.0 - 1.4 in one day. Fish didn't seem to care at all.
    Last edited by Carissa; 11-25-2007 at 12:02 AM.

  4. #4
    Quote Originally Posted by Carissa View Post
    If your pH is only changing from 6.6 - 7.1 it doesn't sound like you have enough co2. I could be wrong but I'm pretty sure that with a change that small there's no way you could be injecting enough co2. But if you have low light it won't matter all that much.
    The change in tank water pH in relation to the CO2 saturation is irrelevant. You cannot compare the pH change in one tank with the pH change in another tank. That's why a drop checker is used with 4dkh water. It's only the pH change in the drop checker that indicates the level of CO2 saturation. Having said that, a tank water pH drop of .5 is roughly a 3 fold increase in acidity so that is not a small change by any means.

    Cheers,

  5. #5
    I have never found that my CO2 concentration drops all the way to ambient values over night. I have quite a bit of surface ripple from my spray bar, just to make sure it does drop a significant amount, but the drop checker is only blue green in the morning, not blue. So, a .5 drop in pH when you add CO2 the next day could very well mean 30 ppm of CO2 in the tank, or it could be more, or it might even be less.
    Hoppy

  6. Quote Originally Posted by ceg4048 View Post
    The change in tank water pH in relation to the CO2 saturation is irrelevant. You cannot compare the pH change in one tank with the pH change in another tank. That's why a drop checker is used with 4dkh water. It's only the pH change in the drop checker that indicates the level of CO2 saturation. Having said that, a tank water pH drop of .5 is roughly a 3 fold increase in acidity so that is not a small change by any means.

    Cheers,
    But to get up to 30ppm with only a .5 difference in pH you would have to start out with 10ppm before adding co2 which at least to me doesn't sound very possible. I could be wrong there about the chances of having 10ppm to start off with, but from what I've read, 4ppm would be on the high end for water that has equalized with the atmosphere. But if the water chemistry is changed in any way between the two pH readings other than adding co2, that will mess up the results of the correlation between pH drop and co2. Someone correct me if I'm wrong, but I was under the impression that x amount more of co2 will always cause the pH to drop x amount irregardless of anything else that is or isn't in the water to start with assuming that's the only variable being played with.

    Anyway I was thinking that the pH was 7.1 before adding ANY co2, if that's just in the morning, that's different because you don't know if it's at equilibrium at that point yet or not like Vaughn said.

  7. #7
    The pH/KH/CO2 relationship is not valid in tank water which has other acidic components in the water affecting the pH. The relationship is only ever valid when the contribution to acidity is due to CO2 alone. A drop checker using distilled water, and which is absolutely free of any other acids has it's pH change ONLY as a direct result of the dissolved carbonic acid. If you use tank water in a drop checker then you may as well not use a drop checker at all since this sample water is corrupt. If you calculate CO2 by merely using the tank water pH as a basis for your calculation then whatever number you calculate for CO2 is also totally corrupt.

    It therefore does not matter that ayhy2mark33's tank water is 7.1 in the morning, or that his pH is 6.6 later on. These measurements tell you absolutely nothing about the precise CO2 content. It only matters what the pH of the water in his drop checker is. After adding CO2 both the drop checker's sample water and his tank water will experience a fall in pH. The difference is that his drop checker water's pH will fall in proportion to the CO2 in accordance with the relationship, whereas the water in his tank will fall in accordance with some other relationship that is of no use to us.

    Hope this helps to clarify.

    Cheers,

  8. #8
    Wow tons of information in here. Thanks to everyone that replied. I am glad to hear that my logic was correct in this.

    Should I be adding more Co2 than I am adding? I have plecos, 2 flounders, a ropefish, a black ghost knife, and some aeneus (sp?) corys. I didn't want to go TOO low in Co2 as this DID happen once when I accidentally went into the yellow and my fish almost bit the dust.

    I am acheiving green levels in my drop checker, but I guess I could add more, even though I am already at a rate of 3 bubbles per second with the ONLY surface agitation during daylight hours being a surface skimmer.

  9. #9
    Hi,
    Glad you find the info useful. If your plants/fish are doing well and if you don't have any algae problems then I don't see any reason why you should worry about what the pH values are at any time. Chasing pH values will only get you into trouble and "natural pH" doesn't mean anything. Your plants and animals are trapped on stage in a glass box, electrically heated and lit with Hollywood bulbs. There is hardly anything natural about that. There is not much to be gained by focusing on pH. Focus more on clean water, regular tank maintenance, proper dosing schedules and stable/adequate CO2 and you'll be fine.

    Cheers,

  10. #10
    Myself and Amano seem to have parallel paths here, we both turn CO2 off every night in every tank we do. I asked him why years ago, he just said "it was Taboo in Japan". Not much of an answer. We both think this independently and came to this method long before we met or knew of eachother.

    1#
    I have my reasons for not doing it at night: common sense says, it's just not needed.
    Waste.

    2#. Error, I can get away with adding more during the day when it's most needed without overdosing the fish and O2 is only produced during the day(never at night).
    this allows more CO2 and more O2 and less CO2 and less O2 concentrations to coincide..........not high CO2 and low O2.
    That's bad/worse for fish than any nutrient other than a few trace metals and NH4 etc.

    I find it odd some will howl over 30ppm NO3 being too high, toxic, bad for fish etc etc etc.......yet feel no issue adding 30ppm of CO2.

    CO2 has killed far more and is far more toxic than NO3, PO4, or K+ to fish.
    But they do not give it a second thought, there is no Fear mongering going on with CO2..............

    I've never quite understood this.
    The logic is missing me here.

    CO2 can change rapidly and go from 2ppm to 30ppm inside 1 hour, and it can cause algae and other secondary issues. Given that, unlike NO3/PO4/K etc all which do not change much over the same time frames...........CO2 is obviously much more critical.

    Also current is a huge issue, do not reduce current to save/conserve CO2, you will reduce the O2 which is much more critical to fish health.
    With good current, you also have better CO2/O2 exchange with the plants.
    We can always add a bit more CO2 during the day to make up for any losses.
    It's cheap and we are not adding it at night.


    Regards,
    Tom Barr

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