co2/O2 please explain.

[boilermakertom]

I'm trying to educate myself before trying a planted aquarium. I think I have this right. To make sure fish in an unplanted aquarium have enough oxygen the water surface needs to be agitated to some degree. To keep CO2 in the water: surface agitation needs to be minimized. I just don't understand this. Could someone please explain this to me. How does bubbles/splashes get oxygen into the water when the same action forces Co2 out?

 

[DoctaQ]

splashing or any surface disturbance will equalize the concentrations in the water with those in the air, co2 in the air is say 2ppm and say oxygen is 4 ppm, if fish live in the water say they are producing .5ppm co2 per hour and use .5ppm oxygen per hour. if you are not injecting co2, disturbing the surface will bring those levels back to normal. i just made these numbers up by the way.

when you inject co2 to 20ppm disturbing the surface will bring it down to 3 ppm, wasting your co2. oxygen levels are independent of co2 but during the day it will also be high if you are injecting co2 because the plants are producing it.
the only problem is at night when plants are also using oxygen and not co2. some higher end tanks will run an airstone at night.

 

[boilermakertom]

so the splashing is just equalizing gas amounts? I think I get it. So Why do you need extra CO2 to grow plants in an aquarium when you don't need it for houseplants?

 

[Brilliant]

If you think of it that way you dont really need co2 to run planted aquarium.

I took notice that moving of current at the top of the water without agitation promotes gas exchange but has little impact on co2 level potential.

So my spray bars and koralias are pointed upwards slightly causing slight disturbance in top of the water but no white water. This has proven to be enough for all tanks full blown or low tech.

 

[tanker]

so the splashing is just equalizing gas amounts? I think I get it. So Why do you need extra CO2 to grow plants in an aquarium when you don't need it for houseplants?

1) Gas exchange is only at the surface. Stirring the surface "equalizes" the CO2/O2 content of the water to the air.

2) You do not want surface movement only if you are "ADDING" CO2 to water (Higher concentration in water then air). If you air is full of CO2 then you do want surface movment, because the water will then "absorb" CO2 from the air. *The Osmosis Theary".

3) House plants need CO2 also. If you put a house plant under high light put it into a tent with CO2---It will grow like mad!!!

4) You asked "Why does aquarium plants needed added CO2, but not house plants"
4a) You house plants are not competing for nutrients with algae.
4b) Your house plants just sit there and grow---You are not trying to have it spread over your entire living room.
4c) You "CAN" get away with no CO2 and high lights---Your aquarium plant will act just like a "House Plant". It will not spread or grow too fast.

 

[plantbrain]

so the splashing is just equalizing gas amounts? I think I get it. So Why do you need extra CO2 to grow plants in an aquarium when you don't need it for houseplants?

In water, the rates of diffusion of CO2(or any gas) are 10,000 slower, so when plants start fixing CO2 to make sugars(their "food"), the rate of exchange is very low between the water and the leave compare to terrestrial plants in air.

We can make up for this by adding elevated amounts, or enriched CO2 concentrations, about 20-100X more than normal, this off sets this diffusion rate issues.

We add CO2 to help the plants grow faster and without competition between one another for CO2. Adding CO2 also allows the plants to use the light we add at the highest maximal efficiency possible.

I use the rule of breaking the water's surface: high enough current to move the water really well, but not quite enough to break the water's surface.

Plants and fish both like good current.
This also allows more O2 so the fish can handle more CO2 enrichment without gasping or stress.

When you have a lot of plants, the current decreases a lot more than fish only tanks in general, so more current must be added to have similar O2 and livestock levels.
BTW, enriching the air in terrestrial high value crops in green houses with CO2 is common practice as well, and can increase yields about 30% or more.
Plants still grow also with adding CO2, but just slower, about 10-20X slower in submersed systems typically.

Regards,
Tom Barr

 

[boilermakertom]

I thank you all for your assistance! 10000x? slower is hard for me to grasp. For me the good news is: I'm growing algae without even trying to. So that means I'm already growing plants in my aquarium. So what do I need to do differently to grow larger, more attractive plants?

 

[tanker]

Growing plants in a tank is easier then you think. All plants (algae included) needs two things to grow---light and nutrients (CO2 is included in the nutrient catagory).

Take out one or the other and plants/algae die.

Because plants are better at "absorbing" nutirents then algae---fast grwoing plants keep algae from growing.

Good light makes plants take in more CO2 to grow (Humans get hungry after exercise). Adding CO2 to help plants grow faster and then plants need nutrients--trace, K, ect-- (Humans need vitamins). The higher order plants take all the extra nutrients and the algae starves---(people eat all the food and the rats starve).

Does this make sense??

 

[jpappy789]

An aquarium without CO2 injected will only hold about 2-3 ppm of CO2 with good surface agitation. A lot of the plants in the trade are naturally found emerged, not fully submerged in the water so like houseplants they normally have much better access to atmospheric CO2.

But Mr. Barr pretty much summed it up anyways...

 

[boilermakertom]

I'm learning as I go. It's not plant related-but I learned that my dwarf guarmis think neon tetras are tasty snacks- whoops.