co2/o2 whats the relationship

[FishyMatty]

Is it possible that a heavy fish load can produce enough co2 for a heavy plant load? Does the amount of dissolved co2 have anything to do with the oxygen level. By this I mean, During the day I don't have any surface agitation or aeration so the only o2 is whats produced by the plants. If I were to aerate the water and inject co2 that would cancel each other out right?

[Sammie7]

Hmmm, I'm not all that sure what you're trying to say but, CO2 and O2 are completely independent of each other. So, the amount of CO2 in the water has no effect on the amount of O2 in the water.

CO2 produced by the fish in your tank is negligible compared to that of CO2 injection. A normal level without CO2 injection would be around 1-3ppm, and with it most people try to go for around 30ppm of CO2. If your plants are healthy, they should be producing all the O2 your tank needs in order for your fish to respire.

Do you have any kind of surface agitation? Like a filter that makes the water surface ripple? If so, that should be enough to get O2 to your fish. If not, I would be more worried about the water getting stagnant, but there are planted aquarium that are based off of the concept of letting the plants both oxygenate the water and be the filter. The method is pioneered by Diane Walstad I believe. http://www.bookmasters.com/marktplc/rr00388.htm

Generally when injecting CO2 you don't want a lot of surface agitation, but a little, such as from a filter, if not too intense isn't going to hurt that much.

Did this make sense?

[FishyMatty]

Well here's the thing. My filter outflow is about 2 inches under the surface but its facing at an upward angle creating some but not much of a ripple in the surface.
Maybe my question doesn't make much sense with out some details.
this is happening in 2 tanks. I didn't know that my tap water ph was never the same.(6.4-7.4) and has no measurable kh under 10ppm. so it took some trial and error to correct the problem but after a water change my tank was 7.0 then the next morning it was under 6.0. So my fish have not been happy.

If I don't run a bubbler my fish gasp at the surface or usually breathe heavy.
So what I want to know is...
If I inject co2 and aerate the water at the same time will this be worthless or is the relationship between co2 and o2 different that I understand.

I have a heavy plant load that all seem to be growing fine. But it doesn't create enough o2 for the fish.

I need help here.

[quilaho]

The injection of CO2 has no direct relationship to levels of O2 in the tank. By direct I mean you can inject as much CO2 in the water that you want and it's presence will not alter the amount of O2.

However, the presence of CO2 will enable your plants to generate considerably more O2. Therefore, the CO2 indirectly increases the levels of O2.

That's a beautiful, win-win situation for you. Inject CO2 which raises your O2 and put the bubbler back on the shelf. A minimal amount of surface agitation should keep your fish oxygenated through the night.

[phanmc]

If you inject CO2 while aerating the tank via surface agitation, you will still gain some benefit from the CO2 but you will also be gassing off significant amounts of CO2 and wasting it.

How much CO2 are you injecting?

If the fish are gasping for breath during the night or early morning, you can run an airstone to aerate the water during the time the lights are off. If the fishes are gasping for breath while the lights are on and the plants are photosynthesizing, lower the CO2.

[Sammie7]

Yea, just remember that CO2 dissolves into and leaves the water quicker and easier than O2.

[FishyMatty]

I do use the bubbler at night. But during lights on with no bubbles they gasp. Should I aerate the water and inject co2?

[plantbrain]

A piece of general advice when discussing CO2 and wasting it due to water movement loss and surface agitation, do not worry about wasting CO2 by reducing flow, that is bad and can lead to dead fish.

Plants? So they might not get enough CO2 for the time being, so what? Algae, poor growth can be corrected by adding a bit more CO2 to compensate for the losses and the added flow prevents gassed fish if they add too much CO2, and also mitigates low O2 which can kill their fish.

You can address poor growth/algae issues, you cannot bring a fish back to life. Now think about losing a tank full of Discus or Altum angels that you grew up from babies to large adults......now think about the aquatic weeds that rapidly regrow, cost 1-2$ a bunch after an algae attack or poor growth for a week or two...........

Adding good flow, some surface movement + a bit more CO2 will solve both issues and the tank will be much stable over time. We have to have some movement, and reducing it down to help the plants greatly increases the risk to the fish, a risk I would not suggest anyone take.

It is a wiser approach to add more CO2 rather than less flow.
There are those that go too far this direction also.

It's easy to add a bit more CO2, as long as they are not adding aeration/long drops in the over flow boxes/adding air into the wet/dry sections, torrents etc and venturi aeration and what not, going way too far....then some decent rippling is fine and suggest-able

I'm very leary of advice that reduces the flow to save CO2 unless it is a torrent/aeration etc, good surface rippling, but not aeration/bubbles etc is a good balance.

Also, if you reduce the flow down a lot, then the plants do not get everything they need(CO2, NO3, traces etc), then they will not produce as much O2, that you rely on to off set the reduced flow, then you have gasping or dead fish, no current + no O2 production from plants.

So good current, some rippling /some surface movement, good care for the plant's nutrients, light, CO2 etc can make things very stable and safe for both fish and plants.

It's not hard, just do not carried away too far either direction with the current and error on the fishes' side always here.



Regards,
Tom Barr