Co2 eotd - The Planted Tank Forum
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post #1 of 18 (permalink) Old 09-01-2017, 06:23 PM Thread Starter
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Co2 eotd

Well I am considering the jump to a CO2 addition to my current tank. I have seen the smaller cylinders that are supposedly for paintball guns, and then there are 5lb and 10lb ones and even 20lb ones.

I remember something someone wrote a while back (don't mock it *will* come your turn) about end of tank dump on smaller cylinders, or am I misremembering?

What exactly does that mean, and why would it be more prevalent on a smaller cylinder than a larger one?

The cost is always a factor and usually smaller means cheaper, having said that I would rather save up a little longer knowing I made the right choice and bought a 20lb one that lasted a while and did not kill off the piscine inhabitants.

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post #2 of 18 (permalink) Old 09-01-2017, 06:38 PM
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Use one that fits your setup...
EOTD is not cylinder dependent as far as I know.

2 stage (not 2 gauge) regulators eliminate EOTD (for the most part) though even w/ good 1 stage it is an arguable problem..
running CO2 at the cusp of killing everything is generally not what I'd call a good idea btw..

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post #3 of 18 (permalink) Old 09-01-2017, 07:08 PM
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EOTD is not something to really worry about. You don't need to spend a ton of money on a two-stage for this reason. I have 2.5 and 5lb cylinders with inexpensive one-stage regulators and never once experienced EOTD in probably 12 years of doing this. With all the aquarists on this forum you would see a thread everyday. "EOTD - Killed all my fish".

I let my cylinders go completely out before refilling without issue.
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post #4 of 18 (permalink) Old 09-01-2017, 07:33 PM
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Quote:
Originally Posted by houseofcards View Post
EOTD is not something to really worry about. You don't need to spend a ton of money on a two-stage for this reason. I have 2.5 and 5lb cylinders with inexpensive one-stage regulators and never once experienced EOTD in probably 12 years of doing this. With all the aquarists on this forum you would see a thread everyday. "EOTD - Killed all my fish".

I let my cylinders go completely out before refilling without issue.
So why then do so many warn against cheap regulators?

And what is a good single stage regulator?
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post #5 of 18 (permalink) Old 09-01-2017, 07:48 PM Thread Starter
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Thanks for the prompt replies guys, as a result of the encouraging responses I called the local Dicks sporting goods store for prices on cylinders, guy was super nice and uber excited because I mentioned CO2, he said yeah we have some 20's in and I fill them four times and the fifth one is free, wonderful thinks I. What is the cost I ask? He says $23, yes they are on sale at the moment.

I am seriously trying to keep the excitement out of my voice at this point! Then he says we also have TEN OUNCE cylinders with the same deal. Down to earth with a bump!

Note to self. ENSURE TO ASK FOR **20 POUND** CYLINDERS IN THE FUTURE!!!!

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post #6 of 18 (permalink) Old 09-01-2017, 08:03 PM
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Weigh the cylinder when full with the regulator, then weight it when the pressure starts going down. You will know exactly how long you have.
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post #7 of 18 (permalink) Old 09-01-2017, 08:13 PM Thread Starter
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Weigh the cylinder when full with the regulator, then weight it when the pressure starts going down. You will know exactly how long you have.
Good idea ChrisX, I shall remember that!

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post #8 of 18 (permalink) Old 09-01-2017, 08:29 PM
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So why then do so many warn against cheap regulators?

And what is a good single stage regulator?
Usually cheap regulators come with in-precise needle valves which sometimes makes it hard to keep a bubble count steady. This is usually an issue on small nano size tanks were the bubble count can't be slowed enough. Many times it's user error in that they don't raise the working pressure high enough.

This has nothing to do with EOTD.
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post #9 of 18 (permalink) Old 09-01-2017, 10:03 PM
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If you are even thinking about going larger than a 20 or 24oz paintball, go for it. A decent regulator will work on a 2.5lb (which is the smallest standard tank for CO2 I believe), which is bigger around, but not much taller than a paintball canister.

Another route to look into for dual-stage - I went the ebay+post-reg kit method, and I am extremely happy I did. For $130 + cost of tank/fill, I was able to build a high quality dual-stage kit that is easily modified and maintained. But it does take some research on part numbers for regs, but not hard to find with patience. Used lab equipment is often the best place, as they are not listed as aquarium equipment, but are perfect for our use (We need a on-going sticky with all the regs to look for)
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post #10 of 18 (permalink) Old 09-01-2017, 10:29 PM
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Some thoughts on smaller versus larger CO2 tanks. The reg is a pretty simple minded item and many do use single stage, dual GAUGE regs. EOTD is short for the theory that as the last of the gas in the cylinder is used up, single stage reg lose the ability to control the output pressure and may force too much CO2 into the tank, killing fish. One sure way to avoid this is to refill the tank before it goes totally flat!!!
That gets into what size cylinder. A small tank costs less upfront but bites you hard when it does get low. It gets low too often, refills normally have to be done at specialty shops where the gas is super high for the amount. You normally pay more for the labor it takes than the gas itself. Check local area for the price to refill at someplace like a brew shop versus a welding gas supply to see how your area works. Then add in the time effort of getting it taken apart, to the shop, filled and back again. Driving time has to figure into this.
But one reason for larger like 10 or 20 pound is the way we humans tend to screw up. We tend to break things or leave leaks and that can really mess up the cost saving if you leave a small leak and squirt the gas out in the room rather than the tank!
I use 20 pounders as I have the room but ten is a good one also. Five pound if a small aquarium or space is a premium.
The 20 oz?/ Not for me.
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post #11 of 18 (permalink) Old 09-01-2017, 11:12 PM
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24oz PB tank last a month at 3bps = 30+ ppm in a 50g tank. It gives me about a week once the pressure starts going down to where it is near empty. When the tank pressure is just a bit above working pressure, I found I still have 1.5oz left. I have not tested EOTD theory. Cheap $40 ebay regulator works great.

Advantage of small tank; if there is a leak, you are only out 5 bucks, not 15-30.

I'm not unhappy I went with paintball, but not suitable for anything over 55g. Multiple paintball tanks are about as inexpensive and convenient as a 5# tank and refills are cheap and plentiful. Only 10 and 20 gallon tanks end up saving money.
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post #12 of 18 (permalink) Old 09-22-2017, 10:53 PM
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I am not an expert on gas physics, however I do have an observation about the illusive EOTD. CO2, as I understand it, is not like other gasses - like the tanks you get filled with air for scuba diving. Those are filled according to PSI as air remains a gas under pressure. CO2 and Propane however are measure in lbs. This is because the gas turns to liquid under pressure. You can observe this by pouring really hot water down the side of a half-filled propane tank and you can feel exactly where the level is because the liquid will absorb the heat from the water below the gas line. Hot above, cold below. CO2 remains at a steady pressure somewhere around 870psi as it is "boiling" off within the cylinder. You can measure that the overall weight of the cylinder will decrease as you use it, but the PSI will remain steady. At the end, the PSI will decline to your setpoint ( I run about 30psi on the low side) on the reg, but I am uncertain if any "extra" gas will get past it. I have read, but cannot confirm that some regs, if there is not a certain minimal amount of pressure on the high side, will vent to the low side at that minimal pressure. If that "minimum" is something like 60psi, your bubbles at the counter I suppose could be 2x as large because of the added pressure at the needle valve. But, I would think that the needle valve itself provides a pressure drop across it as well.

Thoughts?

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post #13 of 18 (permalink) Old 09-23-2017, 02:36 PM
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If EOTD is real one thing is for certain, you're twice as likely for it to happen with a 5 lb tank than you are with a 10 lb tank.
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post #14 of 18 (permalink) Old 09-23-2017, 08:03 PM
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Quote:
Originally Posted by Kubla View Post
If EOTD is real one thing is for certain, you're twice as likely for it to happen with a 5 lb tank than you are with a 10 lb tank.
Why is that?

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post #15 of 18 (permalink) Old 09-23-2017, 08:41 PM
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Here how EOTD happens - for real! Normally the pressure at the inlet enters the chamber and pushes against the diagram and Spring "A" thus allowing the red orfice to close. Flow happens in two situations. One is the outlet pressure drops - as in a normal flow setting where the solenoid is open and gas is flowing like it should. Or there is no longer enough pressure at the inlet to push against the spring as when the tank connected to the inlet drops below the EOTD pressure. There is 100psi, for example, free flowing though the valve because there is no longer enough pressure to shut off the orifice. Only the solenoid after the regulator will halt the flow. The moment it opens back up, it will flow at the 100psi instead of what we set it to - like mine is set at 30psi. The needle valve will receive 3x+ the amount of gas and allow a proportional amount on thru.

Hope this helps someone. Of course please do chime in anyone if you can add additional / more correct light ;-)

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