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Discussion Starter · #1 ·
My first post, I found your forums through a link on AquaBotanic's website. Very interesting and somewhat helpful (most of you guys are running tanks well beyond my current ambitions though, so somewhat over my head).

I am making plans to convert our office's current fake plant tank into a planted one. I'm planning on 1.5-1.75 watts per gallon for lighting on a "heavily planted" tank. Low-light/CO2 requiring plants. However, I'd still like to get the most growth, development, and health out of this tank as possible. I imagine the main limiting factor for the tank will be CO2 levels. Meaning, I could use low-light plants under my lighting and supplement a wee bit of CO2 and see better growth. I'm not gonna do that, yet.

My question is on surface disruption and CO2 levels for this tank. I've read a thousand times in all my research that surface disruption depletes CO2. I get this much, and am planning on converting from a cheapo hang on filter and air stones to no air stones and a canister filter to calm the waters. The calmer the water, the more CO2 your tank will aquire from the surface atmosphere.

However, I found another thought on the subject that points out that air stones and other sources of surface disruption actually create a baseline CO2 level and does such at a rapid rate...that which will be there in say any ole bubbly stream. If your CO2 level is below that amount, surface disruption actually adds CO2. And a perfectly calm tank allows for only slightly more CO2.

So, is there a situation where you would want surface disruption? Lots of plants taking out CO2 and depleting the CO2 below the level a bubbly tank would keep it at?

Thanks for your help.
 

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Ok, so here is how I see it (but please correct me if I'm wrong:slywink:)

If I understand well, you are planning to go with "low-light hight-tech" - 1.5-1.7wpg + CO2.
Since you are adding CO2, you wish not to lose it, and yes, both air stones and HOB will contribute to CO2 loss - therefore in order to reach desired level you'll have to pump more CO2 in the tank. The CO2 does not dissolve in water very well, and the splashes from HOB, or air bubbles provide large contact surface of your CO2 with air - and that is where your CO2 will run away before it can reach/be used by your plants.

For most people with no CO2 injection it should not be a problem - and you are right, there is a balance and steady state levels of CO2 in the water.

Now the surface disruption(as you call it) and surface agitation, at least in my understanding are 2 different things. You'll get splashes and bubbles - which disrupts the surface, but what you really need is good water circulation and agigation in the tank to distribute all the nutrients, CO2 and stuff to the plants. This also ensures good gas exchange on the surface of the tank (which is very important if it goes for fish or bacteria), but your loss of Co2 will be much lower.

Lol, hope I made sense hehe. Cheers.
 

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If you're adding CO2, you want some slight evidence of water circulation at the surface of the tank - a subtle standing wave or slight but persistent ripple - no more than enough motion to assure you that your tank isn't going to slowly go hypoxic.

If you aren't adding CO2, go a head and use airstones, HOB filters, fountain heads, paddle wheel boats on the surface - whatever you want, it helps keep the CO2 *up* to 3ppm. 3ppm is the baseline level that can be maintained in a tano w/o CO2 addition if there is adequate gas exchange (aided by surface agitation). Without surface agitation, plant consumption of CO2 will bring levels even lower.

If you're adding CO2, your target is 10x this baseline level.
 

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Discussion Starter · #4 ·
No i am not adding CO2. sorry you got that impression juso. I just meant it'd be better if i did. i'm not going to.

Squawkbert...you're saying that if the tank isn't getting added CO2, it's actually better to have rough waters?

Thanks for your help.
 

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I think what Squawkbert ment is that if you are not going to add CO2 it does not matter.
You DO need water movement in the tank, but since you are not adding CO2, you can use HOB, air stones and whatever.
For my low-tech I'm getting enough water agitation just with HOB - no need for air stones or paddle wheel boats :)
 

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Discussion Starter · #6 ·
here's a thought i figured i wouldn't create another thread for...

suppose i got the wimpyiest of wimpy air pumps going with an airstone that produced the tinyest bubbles i could find. one of thoes wooden ones, or something suitible for a protein skimmer. and then put it under the cansiter filter's outlet so many of the little bubbles get knocked around the tank for the longest time.

i realize that there is very little co2 in plain "air"...but, if i'm doubling or trippling the air/water surface of the tank with these little bubbles, won't i increase the dissolved co2?

in my imagination this weak air pump combined with the tiny bubble stone will result in almost no surface adgitation...am i dreaming on that point?
 

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Any airpump with any airstone will result in a decent amount of surface agitation. Enough to maintain the 3ppm of CO2. It would help preserve CO2 levels if a tank that you were adding CO2 to, versus say, using lots of airstones and biowheels.
 

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Always knew that surface disruption would oxygenate the water more per say, but never thought about the fact that it would also be expelling CO2. Ahhhhhhh, so much to learn, so little time!!!
 

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Any airpump with any airstone will result in a decent amount of surface agitation. Enough to maintain the 3ppm of CO2.
Water in equilibrium with air has about 0.5ppm.

The 3ppm claim is unique to the planted tank hobby. Every other discipline and science states 0.5ppm. Just one example out of dozens I could post, scroll to the bottom:

http://www.gewater.com/handbook/ext_treatment/ch_4_aeration.jsp

If you learn the applicable formulas and compute water CO2 content at equilbrium with air, you'll also get 0.5ppm. I once spoke with someone who claimed he did it and got 3ppm, and said if I show him my math, he'll show me where I went wrong. I showed my math, and asked him to show his. He never got back to me. :)

Nevertheless the 3ppm claim is believed and repeated. I'm not sure where it came from originally, been looking for the exact origin of that for a while. Might be Steve Dixon, but he's since retracted it:

For years I have commented on the APD that the "equilibrium" level of CO2 in the water column of aquaria is between 2 and 3 ppm. Using the chart, I have always observed this level of CO2 in my tanks if I turn off the CO2 system. A couple of months ago George Booth pointed out correctly that the equilibrium level of CO2 and water is under 1 ppm. The 2 - 3 ppm that I observe in my tanks includes a small amount of CO2 being generated by the bioload in the aquarium (fish waste, decaying plants, peat granules and the like)."

And if that's not enough name dropping, Diana Walstad seem to agree too:

I stand by my statement that water in equilibrium with air is 0.5 mg/l. My Limnology reference book by R.G. Wetzel states (p. 202) that "the amount of CO2 dissolved in water from atmospheric concentrations is about 1.1 mg/l at 0 degrees C, 0.6 mg/l at 15C, and 0.4 mg/l at 30C."

Sorry for the rant, but it's a pet peeve of mine. I wish the 3ppm myth would die already. Folks hear it and get the impression that if they aerate heavily, they will "maintain" 3ppm. Sounds like a sweet deal, the plants should get a some benefit from it, since it's a tenth the CO2 of a typical CO2 injected tank - and it's inexhaustible and free!

But it just ain't true. You cannot gain any useful amount of CO2 through aeration. Even in a non-CO2 tank. Because if you do have 3ppm from bioload (as Dixon described), aeration is only driving that out of the tank, towards the real equilibrium of 0.5ppm.
 

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It sounds like your goal is to get good plant growth without adding CO2. Don't worry about surface agitation. Instead focus on getting the right plants. There are many species in this hobby that do great with no CO2. Crypts, Hygrophila, Sagittaria, the list goes on and on.

Surface agitation WILL help keep surface scum from forming.
 
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