# What should my Co2 gauges read?



## Barbels (Aug 3, 2004)

I use the Milwaukee Co2 regulator. What should my gauges read?
I decided to really crank up my Co2 and shut it off at nite. It is giving the algae a darn good butt-kicking.
However, after tonite's w/c I noticed that the high pressure gauge on the left is very low. The needle is only about 2 little dashes above zero (if that makes sense)should it be this low? I do not remember it being this low before. The low pressure gauge on the right is at 30.
This is a 7 lb cylinder running since October.
It also seems like my bubble counter is going much faster than I set it a few days ago. It usually stays steady as can be. Maybe I bumped it somehow.

Should I turn the big tank knob to increase the high pressure reading? Will I have to then screw around with my bubble counter again?


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## Hypancistrus (Oct 28, 2004)

The left needle should read between 700-800 psi (ideally 800 psi). It only starts to go down when the tank is nearly empty. Once it starts to go down, it will usually end up at 0 within a few days to a week (depending on your bubble rate).

CO2 in the tank is in a liquid state, but once it gets close to being empty, it turns to gas. It's normal for the working pressure (and hence the bubble rate) to _increase_ at this point. So, it's normal to have to adjust the needle valve to decrease the bubble rate in the CO2 cannister's last days before refilling/exchanging.

The right gauge is the working pressure... if your regulator has no knob to control it, you just have to live with whatever it is. 30 psi is a bit high... the higher it is, the harder it is to control the bubble rate. Ideally it should be 15 (between 10 and 20).

I would conclude it's time to refill/exchange your tank.


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## bharada (Mar 5, 2004)

Tank pressure (left guage) is directly related to the temperature of the tank as indicated by the attached chart.

It's safe to say that any reading under 750psi (unless it's winter and you store your CO2 tank in an unheated/uninsulated space) would indicate that the liquid CO2 has been exhausted and you are running on gaseous CO2 only.

As for your working pressure (right guage), I have mine set to ~40psi on my Milwaukee regulator if only to match what I have on my (fixed pressure) JBJ regulator.


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## Laith (Jul 7, 2004)

Barbels said:


> ...
> 
> Should I turn the big tank knob to increase the high pressure reading? Will I have to then screw around with my bubble counter again?


If you're talking about the knob on the tank valve (as opposed to a knob on the regulator) then I have this all the way open. As far as I know, this knob is not used to regulate output pressure but is just an on-off valve...


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## Betowess (Dec 9, 2004)

How big of tank do you have or bubbles per second? That seems like a bit of a short life for 7lbs. Then again if you run it 24/7 that might explain it. bob


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## Barbels (Aug 3, 2004)

Betowess said:


> How big of tank do you have or bubbles per second? That seems like a bit of a short life for 7lbs. Then again if you run it 24/7 that might explain it. bob


Hi. I was wrong, it's only a 5-pounder.
Tank is 75 g's and it always ran 24/7 until a few days ago. I have increased to about 3bps. 

Got it refilled today for $8.00.
I tried my butt off to find food grade and I had to settle for regular old Co2 I get at the welding place. Same place I got it from 6 months ago.

Oh yeah, knob on the tank is wide open. High pressure gauge shows 500.


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## malkore (Nov 3, 2003)

If internal cylinder pressure is only 500psi, either the gauge is broken, or your tank is already of out liquid CO2.

The CO2 cylinder valve should be open all the way. The knob on your regulator should be open to 20psi up to 40psi...then the needle valve dials it to your desired bpm.


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## bharada (Mar 5, 2004)

malkore said:


> If internal cylinder pressure is only 500psi, either the gauge is broken, or your tank is already of out liquid CO2.


Hopefully this reading was taken from a freshly filled (and still very cold) tank.


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## shalu (Jan 16, 2003)

bharada said:


> Hopefully this reading was taken from a freshly filled (and still very cold) tank.


Ditto. It takes a while for the new tank to warm up to room temp and then the gauge will increase to over 800psi. Bill is also right in setting the low pressure relatively high, reduces end-of-tank CO2 dumping risk by a lot.


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## Hypancistrus (Oct 28, 2004)

shalu said:


> Ditto. It takes a while for the new tank to warm up to room temp and then the gauge will increase to over 800psi. Bill is also right in setting the low pressure relatively high, reduces end-of-tank CO2 dumping risk by a lot.


How do you contol the bubble rate with it turned up high? How exactly does having the working pressure turned up high prevent CO2 dumping at tank end?


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## shalu (Jan 16, 2003)

needle valve. I have no problem adjusting CO2 rate with needle valve, I currently set low pressure at 25psi. I adjust tiny bit at a time. Apparently Bill does not have a problem either at 40psi.

At end-of-tank, as high pressure drops, you will notice the low pressure gauge increases, so will CO2 output. That increase is less significant if low pressure is already high, especially percentage wise. However, if low pressure was at 10psi, and it increases to over 40psi, that's 4X! You get MUCH faster CO2 output. You might still be ok if the ph controller funtion perfectly, but we are reading way too many CO2 horror stories even with ph controller.


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## Barbels (Aug 3, 2004)

bharada said:


> Hopefully this reading was taken from a freshly filled (and still very cold) tank.


Hmm, guess it did warm up. It is just a half a hair below 800 right now.


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## malkore (Nov 3, 2003)

bhrada, I didn't even think of the cold tank, as I get mine exchanged rather than refilled, so I never have 'cold cylinder syndrome'. good call.


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