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Alright,

By a tank dump then, you are talking about alot of co2 *gas form* comming
out all at once and sufficating the fish?

I thought you meant liquid comming through and contaminating the water. I
called the welding shop, where I bought the co2 tank, and they said the
liquid could only come out if there was a tub inside the tank, which is
normally only used for large tanks *50gal+* or Paint Ball Tanks.

Which needle valve do you prefer, or is there such a thing?

Thanks!

Dustin
"Chuck Gadd" wrote in message
...
On Thu, 2 Jan 2003 02:58:26 -0800, "Dustin"
wrote:

THanks for the input Cannibul, that I did buy that system. Wish I hadnt
know, maybe I can get a refund.... I dont like the idea of loosing all
the
fish...... was it because he didnt have a needle valve, or because the
product is junk?

The product is perfectly fine. The problem is that the system doesn't
use a needle valve.

But even without a needle valve, the system is SAFE, and works fine.
The issue is what is known as an "end of tank dump". Co2 regulators
are intended to operate with a tank pressure of 800-2000 psi (CO2
pressure will never get that high, it's usually around 800-1000psi).
On the regulator, the high pressure gauge is marked in red from
0-600psi. This is because, when the CO2 runs out, the tank pressure
drops down. The regulator is unable to properly regulate when the
tank pressure is very low. In theory, anything below 600psi is a
problem. In practice, I've run my regulator (from Dave Gomberg) down
to 300-400psi with no "dump". But in any case, once the pressure
drops below the regulators minimum, the regulator looses the ability
to regulate the output properly, and the output pressure will rise.

Since with the "high pressure system" the pressure directly controls
the bubble rate, this rising output pressure results in a CO2
overdose.

At the extreme end, the regulator can completely loose control when
the tank pressure drops very far. At that point, it would vent all
the remaining CO2 in a sudden burst.

For all of these cases, simply adding a needle valve will provide a
safety net.

But, if you keep an eye on the tank pressure, it's easy to notice
BEFORE the tank pressure drops very far. Unlike watching your car's
gas gauge, the CO2 pressure will remain constant (around 800-1000psi
depending on the temp) until the tank is 99% empty. When the CO2 tank
is filled, the CO2 is under pressure, and is in a liquid form. As
long as ANY liquid CO2 remains in the tank, the pressure stays at that
800-1000psi. Once all the liquid is gone, the pressure will start to
drop.

On my tank, with a fairly high CO2 flow rate, I would get about a week
from the time the pressure first started to drop, till it reached the
600psi mark. So even without a needle-valve, if you glance at the
CO2 pressure once every few days, you will see it in time to prevent a
problem.

On my system, with a needle-valve, I intentionally let the pressure
drop all the way down. I run the regulator pressure at about 6psi
normally, and then control the bubble rate with the needle-valve. I
usually have a bubble rate around 2-3 bubble per second. As the tank
pressure dropped below 300psi, the output pressure rose up slowly to
about 15-20psi. I never saw a true "end of tank dump" with a big
spike in output pressure. And the bubble rate (because of the needle
valve) didn't increase much, less than 1 extra bubble per second.

Possibly a bigger issue with the Dave Gomberg high pressure system, if
it's the same as when I bought mine several years ago, is that the
tiny little Eheim diffusor isn't very effective in large tanks. In my
75g, I was unable to get acceptable CO2 levels using it. I ditched
the eheim diffusor, added a needle-valve, and built my DIY reactor,
and I've been very happy ever since.


Chuck Gadd
http://www.csd.net/~cgadd/aqua