Pressurized CO2 tank problem

Hello folks,

I am a newbie to pressurized co2 injection and currently experiencing
some problem with
my setup. I acquired the following set of equipment:

1) co2 tank from welding shop for $55.
2) a single stage dual gauge regulator from Western Enterprised( order
from the same welding shop) $65
3) A Dwyster Flowmeter (Model# RMA-151-SSV) for $44

CO2 tank is connect to regulator. The low pressure output of the
regulator is connect to the flowmeter
using 3 brass NPT threads(Male-Female-Male) without any tubing. The
ouput of the flowmeter is
connect to a brass thread, which in turn can be connect to aquarium
tubing very tightly.

-----------------
Reactor

1) AquaClear Powerheads 402 by Hagen (from Petsmart)
2) A gravel-vac + about 1 feet of its tubing.
3) A wooden airstone

With the AquaClear Powerheads 402, there is an input hole in which an
airline for which an air pump
might be connected to the output of the powerhead. This supposed to
allow additional water+air mixing.
I decided instead of connecting it to an air pump, I connect it to my
co2 tubing. This setup seemed to
work only if I set my flowmeter to a very high flowrate (5-10+ bubble
per second). I realized this happened
due to the fact that I connected the output of the powerhead to the
gravel-vac tube. This increased the
water pressure within the tube and causing water to go up the "air
hole" of the powerhead (This doesn't happened if i do not connect to
the gravel-vac tube). Looking at the "air hole", I decided that it is
possible
for me to pull the aquarium tubing all the way out of the powerhead
output, into the gravel-vac tube, and further into the the gravel-vac
itself. Then I connected a wooden airstone to it. Hence,the airstone
is literately inside the gravel-vac. With this setup, I thought it
would be the same as bubbleing the co2 from
the bottome of the gravel-vac. At the open end of the gravel-vac, I
added some sponges.

I thought with this etup it would be like that of Chuck's setup:

http://www.csd.net/~cgadd/aqua/diy_reactor.htm

Still, after I adjust the co2 bubble rate to about 5 per sec. without
the powerhead on; the result is quite the
same. The result is that no bubble would appear after 1 or 2 minutes
after the powerhead is turned on. I believed the water pressure
somehow restricted the CO2 to bubble into the gravel-vac. This is true
with
or without the airstone.

And, it seemed that I have to increase more and more pressurized on
the flowmeter or the regulator in order to keep the CO2 bubbling out
of the airstone. What happened now in less than a week is that my
CO2 tank is empty. Also, once the high pressure gauge shown below
850psi, my tank would empty out in
a couple of hour. Before that, the pressure would drop about 200psi a
day. My tank was initally filled to about 1200psi.

I am wondering if anyone know what's wrong and whether the co2
supposed to be empty that fast. One thing about my CO2 tank is that I
bought it from this shop and the guy would exchange a tank for every
prefilled. I asked him whether the tank I bought is tested; he said
that as long as I refill my CO2 there, I don't have to worry about it.
I also asked him about the CO2 tank and how long would it last if I
use it for aquatic plants. He told me that he doesn't really know, but
he think it should last me only a couple of days.

I am wondering if anyone know what's wrong and whether the CO2
supposed to be empty that fast. I welcome any comments and advises.

Joe