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Old 04-26-2007, 05:24 PM   #1
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Can I kill my fish wth DIY CO2?

I am reeaaallly hesitant to add CO2 to my tank. I have read to many crazy stories of fish being gassed to death, pH crashes, and pressurized tanks shooting across the room and killing small children. Oh yeah, yeast splashing all over the place from exploding bottles or the yeast mixture being sucked into the tank. Let's see...anything else that can go wrong?

I've sort of resigned however to doing DYI CO2. I've got the plans and parts and so on but I'm curious about a few things.

The LFS told me that there is virtually no chance of getting to much CO2 in the tank and either crashing the ph or gassing the fish. Is that true?

Will my ph sky-rocket if my yeast reaction expires and I don't replace it right away?

Can I bind the CO2 line that terminates with an airstone right up next to the intake for my Fluval 204 without concern that the yeast mixture will be sucked in to the tank? - I know it isn't the ideal diffusion system but it is a start.

How do I know when a 2 liter bottle is not producing any more CO2? Do I monitor the pH and see when it rises or is there a better way to know when I can unscrew the top and refill with reactive material?


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Old 04-26-2007, 05:37 PM   #2
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There are risks involved anytime you're working with a system that's under pressure. You have to evaluate that, but there are things you can do to mitigate these risks.

In a DIY system, you can add a pressure relief or blowout mechanism. Basically, get a T-connector for an airline, and put a rubber cap on it. That cap will "blow" before one of your bottles explodes.

As for getting too much CO2. Depends on your tank size, but I'd say that's extremely unlikely with a DIY method. In my 20g tank, running 2 2L bottles, I was struggling to maintain 25ppm. It's said that fish are fine until near 100ppm.

If you're concerned about getting yeast into your tank, make a water trap. Get a small 1L or so water bottle, and put 2 fittings in the cap and fill the bottle 1/2-3/4 with water. Put tubing on of the fittings inside the bottl that extends below the water line. Bring the CO2 in on this line, it will bubble in the water and expel through the other fitting out to your tank. If you use a clear water bottle, this can also serve as a bubble counter.

Will your pH skyrocket if it expires. Well, if by skyrocket you mean go back to your supply water's resting pH, the answer is yes. But, this isn't an issue. pH swings from CO2 injection do not affect your fish. This is why pressurized system owners are able to shut off their CO2 at night without the pH swing being a factor.

Monitoring production of your DIY system. If you use a water trap, you'll be able to see the frequency of the bubbles, so you'll know when it slows down or even comes to a complete stop. Or, you'll see the CO2 being diffused into the tank and can monitor it that way. Another way is by testing pH.

If you're going to go the DIY route, I recommend using 2 source bottles. If you were planning on using a single 2L bottle, use 2 1L bottles. On my 20g, I was running 2 2L bottles and couldn't get the levels I wanted, FYI. However, having a 2 bottle system allows you to change them out at different times, so you never go without CO2 injection. With a DIY system, anytime you release the pressure, it takes 2-48 hours to rebuild enough pressure to actually get any injection into your tank. By using check valves and a T connector, you can set this up so you won't lose the system pressure by only removing 1 bottle.

I think I answered most of your questions. Did I miss anything?

Others will give their opinions as well. I will state that I tried the DIY thing for a few weeks, and got overly frustrated by not being able to maintain the levels I wanted and went to a pressurized system. While it's a bit costly, I put my system together for around $160, and now I am able to maintain exactly what i want in the tank.

In the DC Metro Area? Check out GWAPA and WAMAS
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Old 04-26-2007, 06:05 PM   #3
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Neilan had covered all the points extremely well.

I'd like to say that it is possible to get too much CO2 in a tank using DIY CO2, however about the only time this will happen is on the nano tanks with excessive CO2 generation bottles and an extremely efficient CO2 diffusion method. I managed levels above 100ppm in a 2.5 gallon tank by using 2 x 1 Liter bottles with an inline reactor. By cutting back to 2 x 20oz bottles, the levels came back down to the safe range.
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Old 04-26-2007, 06:18 PM   #4
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OK, thanks to you both.
I was planning on using a water trap and a T-valve for pressure relief.

pH swings from CO2 injection do not affect your fish.
Here is a follow up question.
If I'm trying to make the tank more hospitable to some blue rams, who like the water to be a little more acidic than mine, am I barking up the wrong tree with CO2?

Thanks again.
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Old 04-26-2007, 07:34 PM   #5
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It's not an issue with your ph, it is more your kh that will decide that. If your kh remains stable, you will be ok. Since you mention it, what are your current values?
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Old 04-26-2007, 11:46 PM   #6
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pH is 7 or 7.2 and kh is d3.

My pH was so low like 6.4 or below (off the AP chart) that I added some crushed coral to the tank. Now it getting a little higher than I was hoping.

Perhaps I should take the driftwood out and the coral out and see what happens.

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co2, diy, diy co2

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