Tropical Fish Keeping - Aquarium fish care and resources

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steelerfan 05-03-2008 11:02 AM

CO2 Question...
28 Gal, 5 plants, 1 is bamboo, 1 is bacopa(?), don't know the rest. I just set up DIY CO2 and am wondering if anyne might know what a good bubble per minute rate would be?? Right now I'm getting about 20 bpm, it's only been going for about 16 hrs, so it might speed up a little, we'll see. Anyway, any insight would be helpful, thanks!

fish_4_all 05-03-2008 03:51 PM

Wait until you see how it will effect your pH and KH.
Remember, you need at least 3DKH to keep your pH stable and prevent major fish problems!

Go to and download the calculator. It is very useful and I have used it countless times.

klosxe 07-08-2008 11:51 AM

A good indicator of CO2 levels with DIY CO2 is your PH levels. If you have a PH in the range of 6.5-6.8, you are adding the right amount of CO2. If PH goes up, that means that your CO2 levels are getting lower, and vice versa. I would put in a control valve, so that you can turn on/off you CO2 and change the BPM (Bubbles per minute) rate. You should aim at 2-3 Bubbles per Second, or 120 BPM. At night, you should turn off your CO2 because the plants USE oxygen at night when they aren't photosynthesizing. Plus then at night your PH will rise naturally, and in the morning when your lights come on, you can turn you CO2 on, and the PH will slowly fall. You will want to insert a control valve so that you don't over inject CO2, and drop PH too low, and vice versa.

My next tidbit of Info depends on your answer to my next question: Do you have a tight budget, or can you invest some $$ into this tank?

If you can spend some $$, I would invest on a full auto CO2 system. Full Auto means that the system monitors PH levels, and when PH is high, CO2 is turned on. When PH is low, CO2 is turned off and allowed to rise natural. has a great system that I use. This is a little pricy though, but I think it is worth it. If you ever want a bigger tank, this can just be moved over. When your CO2 tank is low, you can take it into a welding shop and they will refill it for you for about 40 $. You only need to refill about ever 8-10 months though. This is the way to go, because the injection system will monitor itself, and you don't have to worry about injecting too much CO2 and dropping the PH too low, and vice versa.

If you plant to stick with DIY, I would definitely find a way to insert some kind of control valve so you can control you BPM. Hope this LONG explanation helps. :)

fish_4_all 07-08-2008 09:00 PM

Make sure that you know the pH of your tank before adding CO2. A pH of 6.5-6.8 could be good unless your pH is normally 8 or 6.2. Use the calculator that I linked to to make sure that things are going right according to the needs of your tank.

1077 07-08-2008 11:29 PM

I may be wrong but I wonder about the safety of turning OFF a DIY co2 unit as was suggested.

klosxe 07-09-2008 03:08 PM

why? plants do not photsynthesis at night, and thus, why add additional CO2 when it wont be used??

fish_4_all 07-09-2008 04:05 PM

Plants can and do take up some CO2 at night and store it for use in the process when the lights come on. Some plants have evolved to the point where they only take in CO2 at night. Yes it is true and no I didn't believe it when I first saw it either. As far as I know there are no aquatic plants that do this but even aquatics can and do take up some CO2 at night for use during the day.

The biggest reason, especially with DIY is because you can have massive pH swings that can kill your fish by starting and stopping it all the time. This can hopefully be taken care of by having a good KH but the risk is high. That is why so many get a pH controller for pressurized systems.

When I used DIY CO2 I never stopped it and did my best to keep the levels steady at all times, even at night. Fluctuating levels of CO2 can be worse than not using at all. I know, been there. My levels would fluctuate simply from temperature changes in my house and it caused more algae than it helped plant growth especially in fall and winter.

klosxe 07-09-2008 04:57 PM

??? What other rescource can you provide to back up your statement??? Plants only use CO2 during the process of photosynthesis. I've never, in my 30 years in the aquarium hobby, ever heard that CO2 is absorbed during the night. I would greatly appreciate some hard evidence to support your statement, which, I personally feel, is incorrect. I am aware that some plants do take in CO2 only at night, but that percent of aquatic plants is miniscule at best. In the natural world, the PH Naturally flucuates from night to day as I described earlier. Isn't the point of an aquarium to provide a slice of that natural world in your home?

fish_4_all 07-09-2008 10:22 PM

The Calvin part of photosynthesis happens continually, day and night. Plants take up CO2 all the time with or without light. The uptake of carbon from CO2 happens all the time so turning off the CO2 at night only leads to pH swings and weaker plants that have to work harder because they did not store up enough nutrients when they could at night.

Like I said, I do not know of any aquatic plants that only take up CO2 at night but they will take it up all night long and this being the case, the more nutrients they can store, the more efficient they will be when they can complete the light dependant part of the cycle.

Might be why most who inject CO2 will leave the systems if they know that it will not harm the fish.

1077 07-10-2008 12:53 AM

I had contemplated using such a system (DIY) to introduce co2 into a ten gal. tank a year or two ago. I was under the impression that one should never attempt to block or restrict the flow of these do it yourself units as co2 is constantly being produced. As I understand it, A rather nasty mess can be a consequence of doing so. I agree with Fish-4-all that shutting off co2 of an evening would result in larger and more sudden PH swings which would be harmful to many fish.

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