when to fill C02 tank?

I am sure that this has been answered numerous times but my search didn't find anything.
I have 2 kegs carbing and my c02 Gauge is about 600, I know that cooling the tank resists in a pressure drop. I am having a party next week and want to know if that amount of gas will last with the 2 kegs or should I have it topped off before?

Thanks
Ian

If its in the red, replace it. Like the gauge says

It's hard to tell exactly how much is in a tank, especially if the tank its inside your kegerator. The gauge is pretty worthless if that's the case. I always have a backup tank just in case, but you should get 7-10 cornys out of a 5lb tank.

When I bought the tank and keg it was about half full. What's the psi on a full 5 pound tank?

Leadpencil said:

When I bought the tank and keg it was about half full. What's the psi on a full 5 pound tank?

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depends on ambient temp. if it's 75 degrees, it can be 800+. if it's 35, it could be 600

Take the tank and weigh it. Total weight minus the tare weight is the number of pounds of co2 left. The tare weight is stamped on the tank.

Thanks for the info, I will pull the tank out tomorrow and check it out.

The temperature in my garage is 28° and my 20# tank is showing around 400psi. It's in the red. I weighed it and I have 9.5# of co2 left. So the tank is about half full. What I do is put a sticker on the side of my tank with the tare weight and full weight on it. I even put the full weight with regulator and hose attached. At any time I can put it on the scale without removing the regulator and get an accurate reading. I use one of the hanging type scales that I use to check propane, and bulk grain measurements also.

I pulled the tank and weighed it. The tare weight is 9-14 pounds. My scale said 13.5 pounds at 37 degrees.

9-14 what the

I thought it was a little strange too. I bought the tank, regulators, and keg off craigslist. The tank read 800 psi.

Your tank is made of steel. It weighs 9lb 14oz empty. If you weighed it without any attachments on it then you have 3.625 # of Co2... it doesn't make a difference on the temp when you weigh. It's almost 3/4 full.

Leadpencil said:

I pulled the tank and weighed it. The tare weight is 9-14 pounds. My scale said 13.5 pounds at 37 degrees.

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Maybe that means 9 pounds, 14 ounces. A tare weight range would be useless. If you've got nearly 4 pounds left, you'll get through several big parties.

The pressure won't go down at a fixed temperature unless there is no liquid CO2 left in the tank. At that time, you will be empty really soon. This is one reason I got a paintball tank (and an adapter to make it fit a regular regulator) as backup.

I have a few 20oz paintball tanks but no adapters for them.
I thought that a full paintball tank was around 1200 psi.

How much more fun it would have been in grade school if the math questions were "Beer brewer Bob has a empty tank designated for CO2, the tank when empty weighs 9 pound 14 ounces. When filled with 5 pound of CO2 the tank weighs... how much? If Beer brewer Bob weighs his tank and it weighs 13.5 pounds how much CO2 has he used ? How much is left in the tank? " Answer to number 1) 14 pound 14 ounces.. Answer 2) 1.375 pounds.. answer 3) 3.625 pounds. Bonus question... is psi stable across all temperature ranges? answer NO... Now this type of questions would have got me more interested in math.

Leadpencil said:

I have a few 20oz paintball tanks but no adapters for them.
I thought that a full paintball tank was around 1200 psi.

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As long as there is liquid CO2 in the tank, the tank pressure will be whatever the vapor pressure of CO2 is at that temperature. At room temp it's about 850psi, and at beer serving temps it's about 550 psi. If you keep the tank at a constant temperature, the tank pressure won't change until all of the liquid CO2 is gone, and the tank is almost empty. Once that happens, and you only have the remaining vapors in the tank, the gauge will drop very quickly. This is why the tank pressure gauge is practically useless for determining how much CO2 is in the tank. It will tell you if you have CO2 in the tank or not, but that's about it. The ONLY way the know how much gas you have is to weigh the tank.