supersmirky

I have a 10 lb tank and the pressure is reading a little under 800 psi but not in the red where it says to order more CO2. When is everyone changing their Co2?

Veloth

I will change mine when it runs out. I'm thinking about getting another tank so I can just swap it out when it's empty.

vancat

You don't want "end of tank dump"!
When the needle drops below the 800 start making plans to refill- you'll have a couple weeks.

I don't think Dave Gomberg will mind me quoting him...

"As you use the CO2 in your cylinder, it gets lighter and lighter. When you have used about 80-90% of the gas, the pressure starts to drop from the 800psi or so it had when it was just filled. If you keep drawing gas, it will drop to zero eventually. But you don't want to do that, because at about 500psi or so, the regulator becomes unstable.
When the critical pressure is reached, the regulator will dump the entire remaining contents of the tank into whatever comes after the regulator. When this happens, the pressure on the output side of the regulator will rise dramatically. You can try to protect your aquarium by putting a pressure relief valve set at 20 psi or so on the output side of the regulator so this excess gas will just be vented into the room that contains the cylinder. If you were dumb like I was the first time, all the gas will be pushed into your tank. If you have a glass lid on it like I did, the "air" space over the tank will be monopolized by CO2, to the exclusion of oxygen. After a few hours your fish will die of anoxia.

Replace the tank when the pressure starts to drop, just like the gauge says. There is another reason to replace the CO2 cylinder when the pressure starts to drop. Catastrophic regulator failure described above frequently damages the regulator itself, often by making a hole in the diaphragm. This damage is not covered under warranty, it is your responsibility to ensure the CO2 cylinder is replaced before regulator failure occurs.

You can tell the tank is running out in a couple of ways. First, keep an eye on the high pressure gauge. When it begins to move off the 800psi or so it had originally, it is time to replace it. Another tool is to weigh the tank. The tare (empty) weight is usually stamped into the tank near the shoulder (ask your CO2 supplier to show you). Add two pounds for the gauge and the rest is CO2. When 80% of the CO2 is gone, it is time to be careful.

Of course the best thing is just to replace the tank. But if you can't do that for a few days, one strategy is to shut off the master valve. One filling of the high pressure side of the regulator will last for several hours (see the section on leak testing). That way, if the tank starts to seriously empty the regulator will not dump the whole thing."

supersmirky

good info. Thanks...I definitely need to change my tank then. I found that my HOme Depot exhchanges the 10 lb tanks for only $13 so, I will be there tonight! Thanks again guys!

vancat

Glad to help.
penny

Seattle_Aquarist

Hi supersmirky,

I agree with vancat, avoid "end of tank dump". I change as soon as the pressure drops below 800 PSI. At that point the liquid CO2 has all been converted to gas and the pressure drops quickly (I run two tanks off of my tank).

Squawkbert

^ agreed, as soon as you see that the tank pressure needle is no longer "parked", it's time to change.

All I really wanted to add is that the whole end of tank dump thing can be greatly ameliorated by using a 2 stage regulator.

supersmirky

And yes, I did have to go look up this word!! lol....i knew what the intention was in the sentence but never heard this word before.

vancat

ooooh! I love learning new words.
ameliorate |əˈmēlyəˌrāt; əˈmēlēə-|
verb [ trans. ]
make (something bad or unsatisfactory) better : the reform did much to ameliorate living standards.

Manwithnofish

At what price? Is this the same choice I had when the popsicle truck came by ...orange or purple?