# Other Aquarium Forums > Equipment and Accessories >  How to check if co2 tank is filled or empty?

## octopus

Just bought a used CO2 tank complete with sol valve and double gauges. I suppose i can call it an auto regulator. Now i am attempting to set up but not sure if there is any co2 in the tank. 1 gauge shows zero while the other indicates 30. No change in the reading when the co2 main knob is shut or open. I dont know if i need to activate the solenoid to do the checking. Will appreciate some advise. I could have checked with the seller but he was not around when i collected item. Tried contacting him but very busy so i am very anxious to get started.

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## Shadow

Full co2 will show around 1000psi on one of the gauge when you open the main valve.

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## hc rotala

It have some decent weight when it filled with CO2. I can feel this when I got it for a refilled.

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## |squee|

Actually, I think there's no real way to know if the CO2 tank is really filled properly or not via the pressure reading.

Reason is, the gauge will show 1000 PSI as long as there's liquid CO2 in the tank. Once the volume of CO2 in the tank decreases to the point where there is no liquid CO2 left and there's only gaseous CO2 inside, that's when you will see the pressure dropping.

from http://www.warpig.com/paintball/tech...namics.shtml#3




> How much liquid is in a "full" tank? Why not fill it up?
> 
> A "full" tank contains about 34% liquid CO2. If it is filled any more, the CO2 will become very sensitive to temperature changes, with a small increase in temperature causing a large increase in pressure. This is a dangerous situation which is avoided by only partially filling the CO2 bottle.
> 
> One cubic inch of water weighs 0.577 oz and the specific gravity of liquid CO2 is 1.977 gm/cc so one ounce of liquid CO2 has a volume of 0.877 cubic inches. CO2 bottles generally have a full-fill to volume ratio of about 2.57 cubic inches per ounce of CO2, so that one ounce of CO2 will take up 0.877/2.57 = 34% of the total volume of the bottle.
> 
> The figure of 68% is often quoted as the volume of liquid in a full bottle, but this error probably stems from translating "ounce" into volume using water as the standard. Water is 1.00 gm/cc, or about half the density of liquid CO2 so that if a CO2 bottle is filled to its rated capacity with water, it will be 68% liquid by volume.


So technically, the CO2 refiller could just refill the tank to anything lower than 34% with liquid CO2 and call it full.

Then again the above is to my understanding and I may be totally wrong.

So yea, imho tell by weight!

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## Shadow

If you want to know how full is your tank, then yeah, you need to weight your cylinder. If you want to know when to top up, look at the pressure gauge.

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## felix_fx2

when the main valve shut if you release the Co2 the guages will drop right... else pressure still remain..
Anyway Squee is correct in essence.... the meter reading starts to drop (faster) is the topup time...

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## octopus

Finally making some progress but still need help. Brought the cylinder for top up. Now can see reading on main gauge at 1000psi. I turned the knob about 1 turn (open) . Switched on the solenoid and adjusted the needle valve. I can see the fluctuations of bubbles in the bubble counter on every turn of the needle valve and co2 coming out of the diffuser. The only problem is there is no change in reading on the secondary gauge. According to instructions i came across, suppose to adjust the working pressure (secondary gauge) to between 5 - 20 psi. But it remains at 40psi. Is that abnormal?. Can i just ignore it and just depend on the bubble per secs on the bubble counter?.

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## Shadow

normal it suppose to be that way.

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## tawauboy

it is normal. that's what a regulator supposed to do; giving a fixed output pressure.
the output pressure may be adjusted if there is some nut, knob or something that allows you to make the adjustment. otherwise, your regulator is a fixed output pressure type.
output pressure is of secondary importance. you are achieving the purpose of having a pressurized CO2 system; consistent CO2 bubble rate.

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## octopus

Good will start with the co2 injection rightaway. Thanks for all those who have contributed to resolving my co2 issues. Have a great weekend!

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