First, I am wondering if the CO2 concentration in the water column (in low tech tank), which is being provided by the organic material in the substrate is at an elevated level? This would be as compared to an inert substrate tank with filtration and no injection. Or does that CO2 come out as depleted by the plants in order to maintain an equilibrium? I am wondering this because I want to circulate a low tech planted tank with an airstone and wanted to make sure that it would not deplete the substrate at an accelerated rate. I have heard that it was fine, so I am not too worried about it, but I also wanted to understand the CO2 process with regard to these processes.

 

CO2 is given off by the organic substrate buried underneath inert gravel. This gas is released slowly and gradually. Provided you have enough number of plants in the tank, everything should be fine. Note the key word is 'enough'. That means in a number that will satisfy the overal equilibrium(ie.plants take up the CO2 from the soil--->plants release O2---->fish and other organic waste sink to the substrate---->plants utilize these as fertilizer---->etc, etc, etc...Don't forget the plants will also give off CO2 and take in O2 during the dark period. This is another equilibrium at play

As long as you don't create too much of a turbulence with your filter, then nothing dramatic should happen. Again, this is all with respect to the low-tech tank with no CO2 injection. Also, make sure you do cover the soil with a layer of gravel to avoid any organic leakage as this could dramatically change the pH as well as other components in the tank.

Paul

 

quote:

Originally posted by Nillo:
I am wondering this because I want to circulate a low tech planted tank with an airstone and wanted to make sure that it would not deplete the substrate at an accelerated rate. I have heard that it was fine, so I am not too worried about it, but I also wanted to understand the CO2 process with regard to these processes.

The more you aerate your system the faster the bacteria will chew up the organic matter. Remember that the soil organic matter has a fixed life span. It is a fact that at some point, the bacteria will have used up the easily digestible organic matter in your substrate. After that its mainly the fishfood input that will provide organic matter to CO2 cycle.

I've noticed that plant growth in my 45 gal has slowed down 3 years from setup. The Cryptocoryne and stem plants are not running riot like they did earlier. I expect this is because there's less CO2 generated by the potting soil substrate. A drop-off in growth is inevitable.

I would use whatever you want to circulate the water, but use the minimum you need to get the effect you want.

 

Thanks for the input everyone.

 

Diana,

I have a question relating to this that maybe your smart mind can answer. I have always thought that since CO2 easily disolves in water and then goes out of solution in water that if you airated the water enough the CO2 in the water would equal the ammount of CO2 in the air.

So if you did that then whatever CO2 the plants would use would be replaced by the CO2 from the air. But I think the trick would be to heavily airate the water to the point of saturation.

I am guessing that a protein skimmer would be a good choice since they are designed to create lots of tiny bubbles and then mix the bubbles with the water. In freshwater you do not get enough foam to make them viable as a filter but its the air that would be good.

I also got the idea to use a CO2 type difuser and instead of injecting CO2 from a steel tank just run a regular airline into it hooked up to a small airpump.

Just a thought, any ideas? Comments?

 

Dear Wally,

I could spend hours researching the answer to your question, which is a good one. However, this has got to be a quick answer.

The air CO2 conc is very, very low-- only 0.035% of all gases in air (mostly nitrogen and oxygen). In general, lakes and other natural ecosystems have more than air concentration, because they get CO2 from decomposition of organic matter.

When you heavily aerate your tank, you drive off all the CO2 in the water, which is usually higher than air concentration.

Your idea is tempting, but if getting enough CO2 to plants were that easy, I think that hobbyists would have a lot less trouble growing plants in their aquariums.

However, all that said....When you aerate your tanks you speed bacterial decomposition of organic matter into CO2. Then you may be adding CO2 to system.

All I can suggest is that if you want to test your theory, let us know what happens!

 

I know of one case when it might make sense to aerate a planted tank for CO2. If the pH is over about 8.4 then there is no CO2 in the tank. Aerating can add up to about 0.4 ppm CO2 (the amount you might get from air) and keep the pH at or below 8.4.

The only way I know of this coming up is in sunlit planted tanks where the plants can consume all the CO2 and start working on the bicarbonate. I imagine it works in ponds, too. Some of us these days might have artificial light bright enough to get the same effect.


Roger Miller