"Drew_Y" wrote in message
oups.com...

The best solution of commercial equipment for planted tanks in the US
is the Eheim regulator with diffuser. I use it in combination with a pH
controller that is almost unnecessary with the stability of this unit.

That's interesting. I orginally started out with an Eheim CO2 system
(regulator, diffusor, solenoid, and pH probe/controller). I was
very disappointed with the system and ended up replacing all of it,
except for the regulator. I would never buy this system again.

Here is a list of things that I think are wrong with it:

- The regulator has only one gauge that shows bottle pressure, and there
is no second gauge for the working pressure. The second gauge isn't
essential but, considering that the Eheim system is no cheaper than
CO2 systems from other manufacturers, I don't see why it couldn't
provide matching features.

- There is no way to adjust working pressure. The working pressure
is fixed by the regulator and the only other adjustment to control CO2
flow is via the needle valve.

- The needle valve is attached directly to the bottom of the regulator.
The valve does not have a handle; instead, there is a small screw
that you have to turn with a small screwdriver to adjust the needle
valve. This is quite awkward because the screw isn't even visible
(the needle valve is mounted at the bottom of the regulator with
the screw head pointing downwards and recessed), and if you
keep your CO2 bottle below the tank in a cupboard (as many
people do), you end up on your knees blindly fumbling around
with the screwdriver to try and find the screw slot.

- The needle valve doesn't have sufficiently fine control. Minute
adjustments on the valve result in large variations of CO2 flow,
making it difficult to set the correct flow rate.

- The needle valve has a tendency to lose its setting. Having set
the flow rate, I repeatedly found that, by the next morning, the
flow had either stopped completely, or increased to the point
where most of the CO2 was lost because the bubbles got
too large and simply burst at the water surface. I got quite
sick of the game of getting up each morning and having to
re-adjust the flow rate, only to find that, by the time I came
home in the evening, the setting had been lost yet again.

- The tubing is attached to the needle valve with a simple barb and,
from there, runs to the solenoid. When the solenoid is closed,
pressure builds up inside the tubing, and there is a tendency for
CO2 to leak between the tubing and the barb. There is no clamp
or similar to secure the hose to the barb. Other manufactures
provide more secure ways to attach the tubing, such as a screw
clamp or a proper push-in hose connector.

- The CO2 diffusor doesn't work all that well. Even when mounted
at the bottom of a 24" tall tank, so the bubbles get a long path to
the surface, quite a bit of the CO2 ends up being lost at the surface.

- The diffusor disk gradually clogs up with algae and debris and has
to be cleaned regularly, which is quite an arduous process. There
are many other diffusor designs that are maintenance free and work
better.

- The solenoid is housed in a separate box with some electronics, and
the box has two small plastic barbs to which the tubing is attached.
The barbs are quite brittle and, after a few months, one of the barbs
developed a small crack, so I had a permanent leak at that point.
The barbs are part of the solenoid valve, so if a barb breaks, you have
to replace the solenoid valve.

I opened up the box and removed the solenoid, and went to Eheim
to get a replacement. Eheim refused to sell the solenoid separately
and insisted that I had to replace the entire control box (including
electronics) at a cost of $155.00. And all that because a plastic
piece worth less than 5c had failed! And the barbs could have
been made of brass in the first place, in which case the entire
problem would never have arisen.

I ended up replacing the solenoid with an industrial-grade one, with
proper hose connections. Unfortunately, the Eheim control electronics
are designed for a 12V solenoid (not a 110/230V one, as is more
common), and can only deliver around 200mA of current, so I ended
up having to add a relay to switch the replacement solenoid.

- The pH control unit allows you to calibrate the probe for the pH 7.0
neutral point, but it does not permit setting of the slope (with a pH 4.0
or pH 9.0 calibration solution). As the pH probe ages, it's slope changes,
but there is no way to compensate for that with the Eheim controller.
After less than a year, the reading on the controller was out by as much
as 0.3 degrees. I contacted Eheim about this and was told that
adjustment for the slope "is not necessary". (Interestingly, the Eheim system
ships with both 7.0 and 9.0 calibration fluids, but the controller has no
mechanism to actually make use of the 9.0 fluid.) Of course, a deviation
of 0.3 degrees is completely unacceptable. (At a KH of 5, that corresponds
to the difference between 12ppm of CO2 and 24ppm.)

- The pH control unit is digital. When power fails, it loses both its
calibration
and the target pH setting (reverting back to a target setting
of 7.0 without any calibration). This is useless -- every time I change a
light bulb or lose power (not uncommon during summer in a subtropical
climate with lots of storms), I have to go and recalibrate the probe and
reset the target value. pH controllers from other manufacturers do not
have this problem and retain both calibration and target setting after
power fails.

So, overall, I think there are too many problems with this system to
recommend it. You can get higher quality and more reliable components
from other manufacturers, and at a lower price to boot.

Cheers,

Michi.

--
Michi Henning Ph: +61 4 1118-2700
ZeroC, Inc. http://www.zeroc.com