GardenBanter.co.uk - View Single Post

30-07-2005, 05:38 AM

In article ,
says...
George Pontis wrote:
You do not require an automatic pH
monitor/controller. Instead you can set it up at some initial rate, say 1 bubble
every two seconds, then adjust up or down as needed to get to the level you seek.
If you know your KH, then you can determine CO2 by measuring pH using your
favorite test method. It may take a small adjustment once or twice a day for three
days to establish your setting, but once done it will remain stable.

I find my that bubble rate varies depending on ambient temperature. The
higher the temperature, the lower the bubble rate. One day, I set my
needle valve for 2 BPS. Ambient temperature was 25 degrees C. The next
day the temperature rose to 30C. I got 1/2 BPS. I set the bubble rate
back to 2 BPS. The day after it went back down to 25C. The bubble rate
was now 4 BPS. This must be something to do with expansion of metal
parts or cheap CO2 valves. I'm not sure if this is everyone's
experience, but I have to use a pH controller to keep the pH stable. It
was just far too much stress without it.

Nikki

Hi Nikki,

A 4:1 change over a few degrees of temperature, that is quite sensitive. And
understandable why you prefer the use of a pH probe and controller. One day I will
have to get one to play with. But perhaps your unit is worse than typical ? The
constant-flow, open-loop system seems to be commonly used, and hardly anyone could
live with that kind of variation.

The instructions that came with my Wilwaukee regulator said that one should open
the needle valve so it is not limiting, then use the regulator pressure adjustment
to set the flow rate. My unit that was not stable with that adjustment. I found it
better to set the pressure to something that could be diplayed on the gauge, say 5
psi, then adjust the needle valve for the desired flow. This has worked really
well for me - it never needs further adjustment. I should note that I have the
solenoid powered 24/7. If one were to plot CO2 over a 24 hr period, there might be
a few tenths change; I have not watched it that carefully. But when I check in the
mornings the pH is consistent and so is the bubble rate.

George