Dissolved CO2 vs Dissolved oxygen levels

[mtchye]

Just a quick question, does having higher dissolved CO2 levels through DIY CO2 affect your dissolved oxygen levels?

I ask the question because i keep a loricariid that is very sensitive to DO levels and I am wondering in my planted tanks because aeration is kept to a minimum - whether that is causing them to be deficient in O2 - if the partial pressures mean that high CO2 causes less O2 to be dissolved in the water?

THanks for any help

 

[aspen]

that is a good question, and many have debated this. some don't bother adding o2 to their planted tanks, because they feel their plants are adding enough, and possibly their stocking is low. myself, i believe that the only way you would know is to actually test o2 levels before lights on in the morning. but, it would depend on what your fishload is, what your plant load is, what photoperiod you are using and also what temp your are running.

ie, the more fish you have, the less o2 you will have in the morning because they are using it. the more plants you have, the more they will use the available o2 in the night. the longer your photoperiod is, the longer the plants will be adding to the o2 levels (to a point), and therefore the less time that o2 will be used up. this is all based on the fact that your plants do start pearling early in the morning, as this is the sign that the o2 they are producing is not being dissolved into the water, and it is at o2 saturation point. the higher the temp, the lower the o2 saturation point is.

however, the easy thing to do is, to put a small air pump, timed to come on a couple of times through the night for short periods, to ensure the o2 levels don't go too low. i was doing this when i had a little heavy stocking in my tank, and i didn't find the co2 was bled off very much at all. if your lights come on at 6 am, and go off at 6 pm, i would time the air pump to come on at 3 am and 5 am for 10 to 30 mins.

i do not believe that high co2 levels block o2 levels directly, but i have read some documentation that high co2 levels block the fishs' ability to use o2, but there is not a lot of references to read on this point nor does there seem to be much agreement on the point.

rick

 

[tjudy]

Do a search on this topic. We discussed this last Fall, and I posted a link to a web site that published a study on it.

 

[mtchye]

Thanks

Hi guys, thanks for the speedy replies. I found Ted's post, just in case anyone else wants to have a read - its here:

http://www.apistogramma.com/forum/viewtopic.php?t=396&highlight=carbon+dioxide+oxygen

It seems that the situation is still unresolved.. the reason i ask is I was reading a book by Larry Vires on Loricariids, and he says that the higher partial pressure of CO2 caused by CO2 injection DOES affect the amount of oxygen that can be dissolved, and this is crucial to loricariids especially since many of them have a low tolerance of low O2 levels.

I guess we'll see. In my experience though, it does seem to have an effect - via increased respiration rate of the fish in the morning. I do tend to have a higher bioload than most people would in a planted tank though.