# Question about CO2



## marvelous (Jul 29, 2006)

I have a completely automatic CO2 with pH controller for my 75 gallon planted tank. Approximately 65% of the aquarium is planted. I leave the lights on for 12 hours a day as well as the CO2 (both are on a timer). I have 290 watts of light and add CO2 at a rate of 1 bubble every second. My KH is 6.5 and my target pH through my controller is 6.9. At these values my CO2 saturation rate should be 24.549 ppm. My question is - should I leave the CO2 on at night and is this too much light versus my CO2 injection.


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## Laith (Sep 4, 2004)

There is no harm in turning the CO2 off at night (or more correctly, at lights out) as the plants don't use it anyway then.

As to your question re light vs amount of CO2 the way to tell is the health of your plants. If they are thriving and little/no algae is in the tank, then there is no need to change your current settings...

With that much light and the addition of CO2 you will want to be adding macro and micro nutrients for the plants as well, which you don't mention.

And welcome to APC!


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## marvelous (Jul 29, 2006)

Thank you Laith for your prompt response. My plants are all doing very well with only a hint of brown algae in the tank - but only on the very lowest levels of the glass and lightly on the drift wood. Nothing is present on the plants. As for supplements, I added a layer of laterite to the substrate when constructing the aquarium as well as slow release fertilizers.. Also every 3 days I use liquid Flourish supplement.


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## Bert H (Mar 2, 2004)

> As for supplements, I added a layer of laterite to the substrate when constructing the aquarium as well as slow release fertilizers.. Also every 3 days I use liquid Flourish supplement.


 What kind of 'slow release' ferts? Are they a product meant for aquatic systems? Many land based ferts contain urea which you don't want in your aquarium. You'll want to maintain macros as: around 10-20ppm K, 10-20ppm NO3 and 2-4ppm PO4 in the tank. The Flourish provides a good source of micro nutrients, but not the macros.


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## marvelous (Jul 29, 2006)

Bert
The slow release fert I was referring to is a Flourish fertilizer that comes in a plug you bury in the substrate when you set up the tank. It is an aquatic fertilizer. I use the Flourish liquid every 3 to 4 days.


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## Bert H (Mar 2, 2004)

Sounds like those are root tabs. I would recommend water column dosing of macros to go along with your fertilization routine, you've got a lot of light there. Check out the EI dosing sticky here for some good info.


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## redstrat (Apr 3, 2006)

If you are using a PH controller for your CO2 injection system there is no real need to turn it off at night, the controller should add the necessary CO2 to stabilize the PH at roughly 6.9 as you have programed it. if that is 24ppm CO2 concentration then you should be fine, your CO2 will probably shut off anyway because it wont be needed to maintain that PH after dark. Why waste your money on a timer but if your more comfortable with a timer then go for it but you wont gain anything other than small ph swings between night and day. 

I'd say your best sign of injecting to much CO2 is your fish hanging out near the surface constantly, possibly even gulping for air, then you know you need to cut it back some. I've had mine as high as 40-50ppm CO2 and just then started to see them head to the surface.

I'd shoot for 30ppm CO2 with your high light, or maybe even a little more. just my 2 cents.


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## eklikewhoa (Jul 24, 2006)

so the only harm from over injecting co2 is less oxygen for fish in the aqarium correct?


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## redstrat (Apr 3, 2006)

No, dissolved CO2 does not displace dissolved Oxygen, it comes down to a principal known as osmotic pressure.. basically meaning fish gills rely on there being less than some certain amount of dissolved CO2 in the water column, if the concentration goes above that point then they can no longer respirate CO2 from they're blood stream back into the water. So regardless of O2 concentration fish can suffocate from to much CO2 in the water. In planted tanks O2 concentrations are often at or above 100% saturation, hence we se pearling. 
I hope this all helps... I could provide some links giving more detailed explanations about dissolved gasses in the aquarium if you think it would help.


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## marvelous (Jul 29, 2006)

Davis
Thanks for the information. I have another question I hope is not too academic for the plant hounds here, but I'll ask it any way. The entire surface of the water in my aquarium is covered in tiny bubbles. I assume this is either CO2 or O2, but I really don't know. Is this normal or an over abundance of something? Is this the "pearling" you were referring to?


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## redstrat (Apr 3, 2006)

it could be both CO2 and O2 depends on how your diffusing your CO2, do you see bubbles coming from wherever your CO2 comes into the tank? Anyway its not all that important if you are getting the desired amount of dissolved CO2 which I'm sure you are because your PH is changing to match the setting on the controller. Anyway, the reason that the bubbles are staying on the surface is because there probably is a small amount of "surface film" which is generally undissolved proteinous wastes. This could be from over-feeding over-stocking or just a new tank... if it doesnt get to bad I wouldn't be very concerned about it. If it bothers you check into a surface skimmerwhich can be had for $10-15 (thats what I use with pretty good success). Another option is to add some guppies or mollies, they like to eat it, but if your already over-stocked, or if they aren't compatable with the livestock you already have, then I wouldn't recommend it because it will only add to the problem. Like I said though its not really a problem unless it gets really thick and gross, it probably even helps you a little by keeping degassing at the surface to a minimum by creating a little barrier.


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## marvelous (Jul 29, 2006)

Thanks again. There are tiny air bubblrs rising from my plants all day long. I assume this is O2 being produced by the plants. All of my plants have the pearling you were referring to so I guess they are receiving the right amount of light and CO2. They all seem to be growing well especially the wisteria and foxglove. Unfortunately, I noticed today some filamentous type algae. Not sure if this is normal. I've only had this tank set up for about 3 weeks now. The only fish I have are 10 otocinclus and 10 Amato shrimp.


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## redstrat (Apr 3, 2006)

If you would like, i could try to ID the algae for you to help work out a solution. Can you post a pic of it, or describe it a little. Maybe that should be a new post in the Algae section. New tanks are especially prone to algae blooms, I have one that I feel I'm finally getting a firm grip on that I've been battling off and on since I started my 75gallon back in April. Usually its just a fert imbalance to blame for algae blooms but there are other causes. Another thing to check out is the AlgaeFinder on APC it can be pretty helpful.


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