View Full Version : DIY CO2 question

06-03-2007, 06:13 AM
I general, how bad is the PH fluctuation when you start adding CO2 with a DIY system?

Is it something that I will need to worry about and monitor, or could I just dose CO2 and not worry about it?

I am currently using excel in my tank, but I am mulling over switching to DIY CO2 when the excel bottle runs out. If nothing else, it would be a good way to compare the two methods.

Thanks in advance for the responses!

Greg Menke
06-03-2007, 11:28 AM
I'm running co2 from a fermenter in our planted tank. It lowers ph from about 7.6 to approx 7. At first I used a homemade bell to trap a co2 bubble underwater, didn't work well at all- the bubble was there but not much co2 made it into the water. It also gave me some siphoning problems- water could easily flow back out the siphon tube. An airstone worked much better and the plants responded immediately.

To get more co2 in, the airstone could be placed under the filter intake, but the plants are growing so well that I don't think I need more at this point.

The fermenter is a 2 liter coke bottle, I get about 4 days of strong action and another 4 or weakening reaction. My receipe isn't stable yet, but there are lots of them online to start with. Any of them will get yeast going, tuning for longevity takes practice.


Lady Hobbs
06-03-2007, 01:04 PM
I ran two bubblers in a 20 gallon and my pH would only drop from 7.6 to 7.4 running 24 hours. I don't know why. I have very hard water so possibly that prevented the drop in some way manner.

Using the airstone with the bubbler confuses me as they claim bubblers deplete the CO2 but yet people use the bubblers to disperse it so this is another concept I haven't understood.

You don't need a bubbler at all unless you are using high light plants.

Come back to correct my blunder! Obviously the co2 is hooked up to the bubbler ....not an air pump. How stupid am I today!!

Greg Menke
06-03-2007, 01:43 PM
Our KH runs about 3, pretty stable. I was suprised by the drop all the way to 7. Its possible the very fine bubbles off the stone (which rise slowly) is getting a lot of co2 into the water. PH has been in the high 6's over the last couple days but given the green water attack I am not inclined to trust it as nominal.

I don't know why an airstone would "deplete" co2 since its just porous stone or ceramic. If its chemically active, then I should think it would do stuff to oxy as well since thats a lot more reactive than co2 is.

If the argument that bubbles from an air stone disturb the water's surface, letting co2 escape, then the solution (if that is considered to be a non-imaginary problem) is to put the airstone under the cannister intake and use it as a reactor so very few bubbles escape to the atmosphere.

Perhaps the co2 depletion argument is made if air going thru the stone is thought to bring co2 out of solution. I'm not a chemist but I should think that would require the co2 to be supersaturated, like a bottle of soda water- certainly not the case in an aquarium.

I think the co2 has been extremely beneficial for the plants- they grow vigorously, little bubbles on the tips of the leaves; much darker green and robust. Which is helpful for procedures like running dark for a couple days, the plants stay healthier.


06-03-2007, 05:01 PM
Airstone causes surface disturbance which releases a lot of CO2 quickly. People do this at night to allow the fish to breathe easier and because plants don't use CO2 at night. But most only do this with pressurized CO2. For DIY, just leave it on 24/7.

Oxygen goes into water very slowly. Most of the benefit from an airstone comes from the fact that is breaks up surface film and creates surface disturbance, not the actual bubbles there are only in the water for a few seconds, so putting it into the intake of your filter would: lead to excessive burping/air buildup (in a canister filter) or not to anything because it gets outgassed right out (in the case of a HOB)

For all intents and purposes, you really don't need to worry about oxygen. You are much better off getting the plants to grow well because they can actually saturate the water with oxygen (past that point, you get the effect called pearling)

pH changes due to CO2 are different from pH changes from buffers, etc and will not harm fish. Case in point: everyone who has a CO2 system does a water change at some point, which drastically changes pH is a very short time (my pH goes from 6 to 7.2ish. No effect on fish whatsoever. The shock is more from the extra dissolved solids when you change pH with chemical buffers.

Assuming you have no other pH changing objects in your tank, you want to aim for enough yeast to cause a 1.0 pH drop. This equals 30 ppm CO2. The amount of yeast needed will depend greatly on your house temperature. I use 2/3 tsp of it now, which held the CO2 pretty steady at about 70 degrees. You'll probably overshoot until you get it right. That being said, it's pretty damn hard to gas your fish using DIY CO2. Obviously if a torrent of bubbles come out, you know you have some issues, lol.

A better way of getting CO2 in is the nano glass CO2 diffusers sold on ebay. They work well with DIY and the diffusion plates produces much finer bubbles evenly compared to an airstone.

Excel is an excellent supplement to CO2 actually. I use it every once in a while to get a little growth spurt and greening.

06-03-2007, 06:32 PM
Thanks for the great responses!!

I think I am going to give it a shot in a couple of weeks. First I want to see how the plants do with a daily supply of excel for about a month.

The tank I will be adding it to is my 12g nano cube, so I don't know if it would be best to add the CO2 into the compartment with water pump. I could easily place the CO2 tube right next to the impeller, and I would assume that would be a good way to spread the CO2 around the tank?

Anyway, thanks again!

06-03-2007, 07:27 PM
I just wanted to add.

I have found that having two bottle makes all the difference. IF you have two yeast reactors and rotate when you change them you get a more constant flow as one bottle is new and while the other is old.

I have a 46 gallon, tank and Have been able to keep it consistently down 1 degree of pH for the last 3 weeks using this method.

06-03-2007, 08:17 PM
Not sure how the nanocube is set up. Does the water cascade into the sump compartment in the back? If so, you may be shooting yourself in the foot trying to set up a CO2 system. If it's a really small waterfall from the spillover, then you will probably be ok. In any case I would just try to stick an airstone/diffuser underneath the media compartments so that the bubbles get trapped in the sponge, etc while the water pushes down.

Lady Hobbs
06-04-2007, 01:42 AM
I added my co2 to an airstone today after reading this thread. Not only is it less ugly, it bubbles better.

06-04-2007, 04:49 AM
I think this picture is the best way to explain how the cube filters work. There is no cascade into the media. Actually, the media sits about 2" below the water level.