# How much notice when CO2 tank is about empty?



## unirdna (Jan 22, 2004)

When the CO2 level starts getting low, the HIGH pressure gauge will begin to drop.

I have a spare tank I keep on hand now. When I didn't, I simply kept the lights off during the non-CO2 days to prevent plant stress.

*edit: Just saw it was your first post, Mike D (Beastie fan?). Welcome to the land of posting - no longer a lurker .


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## ZID ZULANDER (Apr 15, 2008)

Its hard to say. Some regulators come with dual gauges to see the pressure in the tank and that can give you a good idea of how much you have left. The regulators that do not have dual gauges you will have to watch. I did see a sticker type device that you can use on propain tanks I wonder if you could use it on a Co2 tank. Both are liquid and cool so I dont see why not. I might have to try that to see if it will work.


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## Mike_D (Nov 5, 2008)

Thanks for the replies!

I have a dual-gauge regulator, which normally reads between 800-900 psi for the tank pressure. I think I read that when it gets down to 600 psi it's time to get it refilled. But what I was wondering is how quickly that change from 800-600 psi normally happens for people? Is it a matter of days? Or does it happen very quickly? And once you get to 600 psi, will you still have enough CO2 in the tank to keep going for a few days, or does that mean the end is near? I'm guessing at that point there is no liquid CO2 left, so it all depends on the volume of the tank.

I know this all depends on the rate of CO2 you are using, which would be different for everyone, but I'm just trying to figure out how much warning I would have when the tank is getting low since this is my first time with using pressurized CO2. (So I have no clue about how long my tank will last yet.) I'm just worried about the case where it all of a sudden runs out and I can't get it refilled for a few days. But, from what Ted said above it sounds like if I shut off the lights while waiting for the refill, I may be OK.

Thanks,

Mike


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## bpimm (Aug 2, 2007)

As long as there is liquid gas in the tank the pressure will stay at the 8-900 lb reading. Once the liquid is gone the pressure will drop at a rate proportional to your use. I have 2 20 Lb tanks, one runs 3 tanks and the other runs 1. I have 3-4 days on the single tank tank, and the one that runs 3 tanks is less than 1 day.

The best way to gauge your tank is to weigh it empty then refill, then you can weigh it to see how much is in it. That only works if you refill instead of swapping tanks, altho you could establish a rough empty weight for aluminum and steel tanks and they shouldn't vary to much.


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## rich815 (May 21, 2008)

So far my 5 lb'er on my 72 gal has gone one cycle for me. I ran it about the same schedule and bubble count as you and it lasted about 3 1/2 months. When it was running low the gauge that showed 800-900 started dropping over about 2 days to 700, then 600, so I refilled it (actually switched it to a 10 lb now). Based on my experience I think you'll have about 6 months at least with your 10 lb tank.


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## EdTheEdge (Jan 25, 2007)

When I get my tanks refilled the high pressure read in the vicinty of 1000lbs. When it starts to drop I keep a close eye on it. When it reaches approx 700LBS I replace it with my spare. Luckily my Azoo regulators seem to prevent end of tank dumps. I've had two EOT dumps and never even noticed until the gauge was sitting at zero......


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## Green Leaf Aquariums (Feb 26, 2007)

I let mine go until it zero's out at 0psi. There is still quite a bit of co2 in a cylinder with 600psi in it.
That being said, Ive never seen a good regulator dump co2. Now I cant say the same for overseas type regs.

Regards, Orlando


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## EdTheEdge (Jan 25, 2007)

Orlando said:


> I let mine go until it zero's out at 0psi. There is still quite a bit of co2 in a cylinder with 600psi in it.
> 
> Regards, Orlando


Good point...but not all regulators have a pressure release valve and an EOT dump can be disasterous.....

I change mine out at about 700 LBS because I know I will only have about a week or two maybe three until it empties completely.

It's good to have a spare tank in the garage. I have a 5LB that I keep as a spare and use 10LBers on all my tanks.


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## unirdna (Jan 22, 2004)

Here's a handy baseline for you, Mike.

For a 5 lb CO2 tank - 1 bubble per second (1X) for 24hr/day (1X) will last six months.
For a 10lb tank --> one year

So, for 8 bubbles (1/8X) per second for 8hr/day (3X), your tank will last:

One year x (3/8). 3/8ths of a year = 4.5 months 

IME, at the rate you are running, you'll see the high pressure gauge drop to zero over the course of about 2 weeks.


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## Mike_D (Nov 5, 2008)

Thanks for all the advice! This forum has been really helpful. I've learned a lot here.

It sounds like I'll have a good amount of time to get the cylinder refilled after I see the tank is getting low so I don't have to worry about being able to get it filled immediately.

I went ahead and weighed my cylinder to try and get an idea of how much CO2 I have left. Right now it's about 22 lbs altogether. I don't know the exact weight when it was filled originally, but the cylinder markings show the empty cylinder weight is around 14.5 lbs, and the shipping notice on my regulator showed about 4.5 lbs. So that means I probably have about 22 - 14.5 - 4.5 = 3lbs of CO2 left. I'm guessing that will last about another 4 weeks then, although it's hard to tell since I was originally running it for 10 hrs/day and playing around with the bubble rate, and now I'm down to just 8 hrs/day.


Thanks again!

- Mike


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## EdTheEdge (Jan 25, 2007)

Mike_D said:


> Thanks for all the advice! This forum has been really helpful. I've learned a lot here.
> 
> It sounds like I'll have a good amount of time to get the cylinder refilled after I see the tank is getting low so I don't have to worry about being able to get it filled immediately.
> 
> ...


Just keep an eye on the high pressure gague. It will start dropping quickly when the liquid turns to gas....


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## rich815 (May 21, 2008)

Mike_D said:


> It sounds like I'll have a good amount of time to get the cylinder refilled after I see the tank is getting low so I don't have to worry about being able to get it filled immediately.
> 
> - Mike


It's not as much time as you'd think. It could be 4-5 days of pressure dropping, it could be 1-2 days. As long as you check it daily whenever you feed your fish as you get close to what you think is the life of the CO2 content and you'll be fine as you'll see it. Just either have a back-up tank or easy access to getting a refill. Be careful about leaving for a 3-day weekend or something around when it might be running low. Stories abound of those who missed it and it went empty on them and they did not catch it. BBA sits just waiting for those moments of serious fluctuating or drop in CO2. You could end up with a serious forest of BBA about 2 weeks later...


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## Mike_D (Nov 5, 2008)

To be safe I went and got myself another cylinder. This time a 20# one. Hopefully that will be enough to last about 6 months, which would be nice. And this way I can have a backup ready in case it's needed.


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