How much CO2

[AlexanderC]

Should I add CO2 24 hours a day, or just when the light is on?

[Komar]

Try this link. There's quite a bit of info about CO2, fish, and plants:

http://www.qsl.net/w2wdx/aquaria/diyco2.html

I leave my homemade CO2 bubblers on all the time, though they really aren't very effective (or consistent). On the other hand, it doesn't take much CO2 to help plants grow, so the CO2 has been very beneficial.

[AlexanderC]

Interesting article, thanks.

[Komar]

I noticed that my pH dropped quite a bit recently. I'm pretty sure this is due in large part to the CO2, though I tested my tap water. The tap water dropped from 7.4 or so to 6.5 over the last several months.

Anyway, definitely keep a closer eye on your pH if you add CO2.

I also noticed that filling the DIY CO2 bottles with very warm water (instead of not so warm water), then shaking the bottle vigorously to mix the contents thoroughly, seems to lead to more consistent results.

However, DIY systems are harder to regulate, so I definitely don't recommend making them too efficient at dissolving too much CO2 into the water.

[Neptune]

I am about to set up a DIY reactor for my tank. From what I understand, it's hard to overdose CO2 with DIY setups unless the tank is very small. For pressurized systems, you can hook it up to a timer so it shuts off when the lights go out, or else use a ph controller.

[Komar]

Good point. My comment about not making them too effective is more to reduce the chance of a radical pH drop, and not so much about overdosing the water with CO2.

My pH drop last week might have been due to the somewhat recent pH drop in my tap water. However, only my 20G tank with a very effective CO2 injector seemed to suffer from a serious pH drop over a short period (about a month). My other tanks (45G and 2.5G) haven't had much fluctuation at all, and my DIY CO2 bubblers in these tanks produced far less CO2 until very recently.

I'll have to keep watch on the pH in my tanks and tap water to be more conclusive. I recommend doing the same when dealing with CO2, just to be safe.

[xoolooxunny]

My DIY C02 is hooked up to an airstone, and i have it set up under a power head intake. that dissolves it A LOT, and also helps circulate it around the tank. I used to have it in the filter intake, but that ended up making rattling noises i guess from air near the impeller.

You shouldn't turn off the C02 at night because it will give you a PH spike.

[Chrona]

With any CO2 system, you need to have a well-buffered water, or else the pH will be high during the day, when planted are taking in CO2, and drop very low at night, when they aren't. Even with a buffered water, you will still see pH differences during the day and at night, so be prepared to take on what you are getting into. By using a clamp on the air tubing, or with various airstone setups (or no airstone at all), you can adjust how much CO2 goes into your system. Increase it slowly until you see a small, but noticeable drop in pH at night vs during the day. This will really be the maximum CO2 you should inject into your water, as any more, while possibly beneficial for the plants, will result in pH swings that will kill your fish.

Ideally, you would have a split valve with your air pump and your co2 reactor going to the same airstone. During the day, the CO2 bottle would be going, and at night, when plants actually use oxygen, the air pump would be going to make sure the fish have plenty of oxygen.

[SouthernGal0682]

Ideally, you would have a split valve with your air pump and your co2 reactor going to the same airstone. During the day, the CO2 bottle would be going, and at night, when plants actually use oxygen, the air pump would be going to make sure the fish have plenty of oxygen.

Ok..dunno if this is a common sense question, but does a DIY CO2 bottle put out enough "air" to be strong enough to push the CO2 through the airstone? I'm used to seeing bubbles pouring out of airstones with an air pump so I was just thinking that the bottle wouldn't be nearly as strong.

[Chrona]

Ok..dunno if this is a common sense question, but does a DIY CO2 bottle put out enough "air" to be strong enough to push the CO2 through the airstone? I'm used to seeing bubbles pouring out of airstones with an air pump so I was just thinking that the bottle wouldn't be nearly as strong.

Yes, it will get that strong. Completely cap a bottle with an active yeast solution and the pressure will get so high that eventually the bottle will explode, since the yeast will keep making CO2 until the alcohol levels in the solution are too high. My mom tried her hand at making wine last summer, and capped a glass container tightly. Needless to say, after a few weeks, the basement was a mess and we actually found chunks of the glass stuck in the drywall lol.

Also, the inefficient DIY diffusers (ie plain airstone) are the way to go if you don't want to have to deal with balancing pH and kH so that your CO2 levels don't kill your fish. If your gas dissolving rate is very high, then you need to compare your pH, kH to a chart to find out the max CO2 possible in your water, which is probably what your tank is at with an efficient diffuser. Then, you would have to adjust the CO2 flow rate accordingly, which is easy for a regulator-tank system, but near impossible for a DIY bottle. With a low efficiency rate, you won't get the ideal CO2 levels, but you'll get plenty for 2-3 watt/gallon lighting and you generally don't have to worry about killing your fish

Oh and perhaps most importantly, test your water's kH. If it is below 5dH, then you need to add baking soda until it hits about that. Anything less, an you run the risk of large pH changes during injection.