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

Discussion in 'CO2 Enrichment' started by sayhy2mark33, Nov 23, 2007.

  1. sayhy2mark33

    sayhy2mark33 Junior Poster

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    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. Gerryd

    Gerryd Plant Guru Team
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    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-planted-tanks/3587-ph-shifts-fish-health-due-co2.html?highlight=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.
     
  3. Carissa

    Carissa Guru Class Expert

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    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.
     
  4. ceg4048

    ceg4048 Lifetime Charter Member
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    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. VaughnH

    VaughnH Lifetime Charter Member
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    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.
     
  6. Carissa

    Carissa Guru Class Expert

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    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. ceg4048

    ceg4048 Lifetime Charter Member
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    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. sayhy2mark33

    sayhy2mark33 Junior Poster

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    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. ceg4048

    ceg4048 Lifetime Charter Member
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    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. Tom Barr

    Tom Barr Founder
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    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
     
  11. sayhy2mark33

    sayhy2mark33 Junior Poster

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    You guys are fantastic. Okay, so I am getting the thought now that I should keep my powerhead on at ALL times to help surface agitation? I can certainly add more CO2, you're right. Please let me know if this is correct, because I'll do it if need be.

    Also, I DO have algae problems. I have blue/green algae in my tank, which I understand is actually often from a lack of nitrate. I run a 4x65w fixture at 10 hours of light, 2 of those hours only running 2x65w (dawn/dusk). Would my CO2 be contributing to this in some way? Please advise.

    I have all rooted/planted plants with sand substrate, so I was going to use a substrate fertilizer system to supply the nutrients, with some dosing as well.
     
  12. sayhy2mark33

    sayhy2mark33 Junior Poster

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    To fix my last message, I ALREADY use a substrate fertilizer system, but not as complex as the new one I'm going to try which uses several different types of tablets to supply the nutrients, along with water fertilization. Didn't want to sound too blank and have you thinking I wasn't already dosing to an extent.
     
  13. ceg4048

    ceg4048 Lifetime Charter Member
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    Hi,
    I would point the powerhead down to get better circulation and really not worry so much about surface agitation. If your fish are not gasping in the early morning without surface agitation then it's really not necessary. Plants produce oxygen during the photoperiod so it's counterproductive to agitate the surface, lose CO2 and then have to increase your injection rate to make up for what's lost because of agitation. The powerhead is much better being used to push the water around and to distribute the CO2/nutrients inside the tank in order to deliver them to the plants.

    Yep, BGA=poor nitrates. You didn't mention your tank size but 260 watts sounds like a lot of light. If you are running low on nitrates then chances are your dosing is insufficient and you are probably low on everything else as well. Without knowing the tank size I can't say how much you ought to be dosing but you'd be well served not to depend on substrate feeding to solve your nutrient problems. With that amount of light water significant water column dosing is probably necessary if your tank size is much smaller than 130 gallons.

    The BGA is already telling you that you are low on dosing...You can't make up for that by adding CO2. What exactly are you dosing, in what quantity and with what frequency?

    Cheers,
     
  14. sayhy2mark33

    sayhy2mark33 Junior Poster

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    Thanks for your reply. My tank size is only 55 gallons. My dosing stinks, I just started this. I don't dose specifics. I use a Kent Progreen formula every 2 days or so, water changes every 2 weeks, about 40%. Also use the substrate formulas. Would upping my dosing get rid of the BGA? Do I need to order Nitrogen?
     
  15. Professor Myers

    Professor Myers Guru Class Expert

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    Carissa, I have to say your instincts and line of reasoning are very impressive. Many of your recent post have been bright articulate and to the point. You've taken to this very well, and that's no small feat given the multitude of variables and rhetoric to sort through. Just my own observations, but really a joy to see someone apply themselves so effectively. Grtz, Prof M

     
  16. Professor Myers

    Professor Myers Guru Class Expert

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    I am personally not a big fan of many of the Kent products as I believe the bulk of them are basic supplements in pretty packaging. As was said earlier you may want to ease up your Co2 and note any differences in the BGA 1st. and then I might monitor your nitrates more closely to recalculate/confirm your dosage. 3 bps Co2 isn't particularly high for a 55 gal. W/ proper lighting. What Temp. do you maintain this tank, and what altitude are you at ? Prof M

     
  17. ceg4048

    ceg4048 Lifetime Charter Member
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    sayhy2mark33,
    260W/55G = 4.7 watts per gall which is a huge amount of light:eek: Trouble is always around the corner if you run a tank anywhere near 3 WPG or above so your dosing really has to be serious and disciplined or things can deteriorate. I don't really know what's in "Kent Progreen formula" I searched all over google and all I found was "Kent Pro Plant" which, if this is the same product contains the following:
    "Deionized water, Sodium Nitrate, Magnesium Sulfate, Boric Acid , humic acid, kelp extract"
    There's some good stuff in it but I'm not sure humic acid and kelp extract will do anything useful. Commercial products have value but you have no control over what's in them and you are usually paying for mostly water. It's not clear how much of the macronutrients (N, P and K) you are dosing by using that product, but those elements and CO2 have to be satisfied first.

    If you want to run your tank with that much light it would be a good idea to check the Aquarium Fertilizer.com link: Greg Watson's Aquarium Fertilizer: Aquatic Plant Food and use the following products in these quantities:

    Potassium Nitrate (KNO3) 3/4 teaspoon 3 time per week
    Potassium Phosphate (KH2PO4) 1/8 teaspoon 3 times per week
    CSB+B (Trace Elements) 1/4 tsp on alternate days
    Depending on your water hardness you want to consider using either GH Booster (1/4 teaspoon per week) or just 1.5 teaspoon MGSO4 3 times per week.

    You should probably do a 50% water change every week instead of every two weeks.

    These are just baseline numbers and you may find that you have to increase these numbers by up to 50% or more.

    Cheers,
     
  18. sayhy2mark33

    sayhy2mark33 Junior Poster

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    Fantastic, I needed it spelled out for me like that. I will try some different things and see how it all works out. Thanks everyone.
     
  19. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    If by 'naturally' you mean prior to ever injecting any co2 then it doesnt sound like your levels are anywhere near 30ppm.

    Irrelevant? CO2 directly effects pH, so long as nothing else effecting pH (acids, buffers) are changing then CO2 is all thats left...

    Again, if CO2 is the only thing changing you should be able to get a number that isnt totally corrupt or absolutely meaningless.

    Case in point, the 1* pH drop method. Doesnt care what acids or buffers you have. If CO2 drops your tank pH by 1* than that is approximately 30ppm (assuming your water only holds ~3ppm naturally). Last I was aware this method was still valid and accurate, has that changed? I verified with my current 75G often by letting a sample of tank water degas for a few days and I get just about exactly a 1* rise (about 6.4 mid day to 7.4 after degas).
     
  20. Tom Barr

    Tom Barr Founder
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    I think given the notion that CO2 is a toxin rather than a mere gas.................
    The way some folks often feel about NO3, PO4, that they must be kept low as possible, and given respiration of fish/inverts as well as increased water clarity that correlates with higher O2 levels..............

    It's fairly wise to shut the CO2 off at night.

    Where it really does not matter is with lower light tanks, tanks that simply do not have much CO2 demand from plants to begin with.

    We often see a hear folks saying they leave the CO2 on all day, 24/7.
    They have decent results.

    So how can we push things to the point where that is not the case?
    Add more light
    Add non limiting nutrients
    Add more plant biomass
    Add better current(delivery of CO2/nutrients increases... well, up to a point))
    Good CO2 delivery system.

    If you look at this list, you'll note I attack each of these and have for many years.
    Many hobbyists seemed to think we know know everything we need to know about CO2. I've yet to meet one that does yet :cool:
    That includes myself.

    If you reduce light intensity, you will have less CO2 demand if the nutrients are non limiting. Likewise, you can reduce CO2 demand by limiting NO3, PO4, K+ etc

    Understanding the play between light, CO2 and nutrients is a key factor in getting beyond all the muckery of many forum discussions. I hope folks gain this understanding and to get a global understanding of aquatic plants.

    What determines our goal and the ranges of CO2 that are safe and how do we make them even safer?

    Clearly, adding it only during the time that we need it is one way.
    So just during the day and perhaps 30-60 minutes prior and maybe when the lights go out or a little prior to that is all that's needed.

    If you use DIY CO2 yeast, then this is really useful in case you over do the brew and have too much CO2 production, the rate of Gas production and delivery tends to be much harder to control vs a gas tank and regulator.

    Some claim and implore the simplicity of adding it 24/7 and lament about how they have troubles with algae doing the on during the day cycling.

    What causes this?
    You should know......

    Poor CO2 delivery/underpowered CO2 reactor/poor mixing in the tank.
    They can achieve decent CO2 only if they allow the system to slowly get there.
    But fast responsive CO2 delivery is unattainable.

    So if they try and add plenty only between a set of times, they cannot do it, it takes too long for the CO2 system to respond unless it's on 24/7.

    Poor circulation often leads to gasping fish when they have 30ppm CO2.
    Many still think and give little consideration to a very basic FISH hobbyist healthy issue: providing O2 for their fish.

    I suppose some forgot about the fish's needs it seems:)

    So go over the list up above and make sure all that is in check and good.
    Then review your test methods and make sure things are good there and feel confident.

    Finally: does the tank look good? Fish, plants, no algae or reduced amounts?

    CO2 is not simplistic in measurement, balance between nutrients, light etc, effects of fish, delivery of CO2 and methods to add it.

    Regards,
    Tom Barr
     
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