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Can Anyone Explain The Carbon Cycle In An Aquarium?

This is a discussion on Can Anyone Explain The Carbon Cycle In An Aquarium? within the Beginner Planted Aquarium forums, part of the Beginner Freshwater Aquarium category; --> Originally Posted by CinBos So do Plants create softer water? Yes and no. They will use some nutrients like calcium and magnesium that contribute ...

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Can Anyone Explain The Carbon Cycle In An Aquarium?
Old 05-08-2012, 06:29 PM   #11
 
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Originally Posted by CinBos View Post
So do Plants create softer water?
Yes and no. They will use some nutrients like calcium and magnesium that contribute to the GH. The process of photosynthesis can soften the water a bit more by removing carbonates, which is why we have the diurnal pH fluctuation in well planted tanks and depending upon several factors this can lower the GH during the day and then raise it during the night, same as the pH rises during the day and lowers at night. But in hard water the effect of all this will be scarcely noticeable.

Mikaila provided all the good techy stuff that you will understand much better than I.
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Old 05-08-2012, 08:45 PM   #12
 
You might want to check this out : CO2: dissolved CO2 and the pH scale | The Skeptical Aquarist

In fact, a lot of articles on this site are really interesting and quite in-depth
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Old 05-08-2012, 10:24 PM   #13
 
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@Mikaila31:

Thank you very much for the equations. The lake is complicated, isn't it? I copied what ended up being the whole thread, unfortunately, and I'll be looking at the two upper pictures until I understand them. Pretty straightforward.

Thanks much.
Steve
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Old 05-09-2012, 12:56 AM   #14
 
Yes they are straightforward when simplified like that. You have carbonates, bicarbonate, and carbonic acid as the 3 main forms of carbon. They dissociate between one another based on the pH which favors equilibrium towards a certain form.

That lake diagram is pretty simplified and only goes up to plants and algae. Its missing any trophic level above that. Plants are made partially of carbon and things eat them, those hetertrophs use respiration and produce CO2 while breaking down the plant or algae matter. They also assimilate some of it. They in turn may be consumed. What consumes them may not be considered to be part of the aquatic ecosystem my most. Say a eagle catching a fish. Thats basically removing carbon(as well as other stuff) from the aquatic system. Like wise trees often fall over into lakes introducing carbon. The cycle very quickly gets very complicated and thats simply from a biological stand point. I am a chem minor and the chemistry part of it is simply overwhelming. A simple arrow on there like the one photosynthesis step is in truth a pathway of 8-10 chemical reactions. The rest are based on cellular metabolisms which are just as complicated. That one figure simplifies 100s of reactions. That how chemistry works. Its cool to learn but the more you learn, the more you realize there is and the less you feel you know.
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Old 05-10-2012, 10:46 AM   #15
 
My Water Params Have Changed A Lot!!

I have no clue as to what's going on in my 10 gallon tank. pH is dropping from 7.3 to 6.8 or .6 and nitrates have gone from 10 to 5.

The buffer may have been exhausted by CO2. I also bought 3 plants, Java Moss, some kind that looks like oriental whatever, and one kind with little leaves and no bulb. Insignificant, I would say.

Please someone enlighen me as to what's going on!

Steve
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Old 05-10-2012, 11:34 AM   #16
 
If you are injecting CO2 then yes it is going to cause a pH drop. If you are not injecting CO2 then the drop is not going to be due to CO2. How much depends on the buffers present in your water. You would have to test GH and KH to really know that. If they are on the low end then that will make your pH easy to fluctuate. Your buffer doesn't normally get exhausted unless it is low to begin with. The buffer is usually dissolved CaCO3 along with some magnesium. Its basically an acid-base equilibrium. The carbonate and bicarbonate are basic. When an acid is added the usually bind it and both are 'neutralized'. The pH will fluctuate somewhat before all the buffers are gone. If the buffers will actually all exhausted pH would hop around wildly.

The plants can explain the drop in Nitrate, but also realized aquarium nitrate tests are very inaccurate.
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Old 05-10-2012, 11:55 AM   #17
 
Thanks Mikhaila,

A good explanation. I just wish I knew where the acid is coming from in my tank. I used Wardley Bullseye 7.0 before I heard about the phosphate in this stuff, and I haven't done any water changes. Just small top offs with tap water. No ingredients on the label.

Steve
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Old 05-10-2012, 12:42 PM   #18
 
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Thanks Mikhaila,

A good explanation. I just wish I knew where the acid is coming from in my tank. I used Wardley Bullseye 7.0 before I heard about the phosphate in this stuff, and I haven't done any water changes. Just small top offs with tap water. No ingredients on the label.

Steve
This is easily answered, acid occurs naturally from the biology. CO2 comes from fish and plant respiration, from bacteria breaking down organics, etc. Mikaila well explained the buffering side. The pH in my tanks is down at 5 since I have no buffers (zero KH) in the tap water, or if I buffer two tanks with aragonite the pH stays around 6.4 (in the 115g) and 6.8 (in the 90g) by design.

As Mikaila said, we need to know the GH and especially for this the KH/Alkalinity of your source water, and tank water if different. The source water will basically remain unless something is specifically targeting it in the tank, like calcareous substances or something.
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Old 05-10-2012, 02:20 PM   #19
 
Thanks for the explanation, Byron. From the most recent MWRA report, Distribution system sample pH ranged from 9.1 to 9.6 and alkalinity ranged from 40 to 42 mg/L. And...

Total Dissolved Solids 35.0

I hope Total Dissolved Solids can help you with GH. The report explains that it is GH.
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Old 05-10-2012, 04:58 PM   #20
 
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Originally Posted by Nemo the Clownfish View Post
Thanks for the explanation, Byron. From the most recent MWRA report, Distribution system sample pH ranged from 9.1 to 9.6 and alkalinity ranged from 40 to 42 mg/L. And...

Total Dissolved Solids 35.0

I hope Total Dissolved Solids can help you with GH. The report explains that it is GH.
That's a fairly low KH, 40 mg/l is roughly equal to ppm, so 40ppm which is approximately 2.2 dKH. I would myself expect the pH to lower as the buffering will be minimal, but Mikaila can confirm or correct this.

So this explains where the acid comes from, presumably?

You also have very soft water, around 2 dGH though this is their TDS and I've no idea how much of this is calcium/magnesium though I would suspect most of it is.

Earlier you mentioned using chemicals preparations to adjust pH, I would counsel against this. It is better to let nature take its course. Forgotten what fish species, but soft water fish will have no issues with just letting it go naturally, although one doesn't want it too low for some. If buffering is necessary, the method I use is safest, in my case just a bout 1.5 tablespoons of aragonite in the filter buffers the 115g and similarly the 90g as mentioned previously. And this lasts years.
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