Re: [APD] Bubbles?

[Andrew Mitchell <andrewm at cse_unsw.edu.au>]

On Tue, 2004-02-03 at 12:51, David Terrell wrote:
> Hi all,
> 
> I was working on making a Co2 reactor for my compressed CO2.  The 
> project only partially failed, I'd like to reverse the flow of water 
> since at the moment the bubbles and water are going the same direction. 
>   Now, that's only part of the story...
> 
> I've only had plants pearl oxygen in the past while doing water changes, 
> never on a regular basis.  Last night after noticing a leak later in the 

At a guess the water you are adding is from the tap and contains a lot
of dissolved gasses. You may notice a similar effect if you pour a glass
of water from the tap... I certainly do. Unfortunately this does not
indicate a large CO2 production by plants.

> evening I just turned off my pump, in anticipation I would fix it 
> tonight.  I came home to find bubbles coming from just about all my 
> plants.  Not an impressive amount as I've seen photographed, but more 
> then I've ever seen my tank produce on their own.  It made me curious, 
> without the flow of water, without the compressed CO2, now they're 
> pearling?  What could possibly be wrong with my setup (wet/dry trickle, 
> 90g AGA overflow) that would cause the plants to seem happier without 
> the filtration + CO2?!

The perling is more related to concentration of O2 in the immediate
vicinity of the plants' leaves rather than general health of the plants.
Without the water flow you won't lose so much CO2 and O2 in your
overflow and wet/dry filter. In addition in an almost stagnant tank
there isn't the water flow to take the high concentration of O2 from the
area very close to the leaves to the rest of the tank, so a high
concentration of O2 can easily build up there.

In general your plants are probably not perling because of losses in the
filter (and overflow) of oxygen. If you have a body of water that is
close to O2 saturation, and aerate it (e.g. wet/dry filter and overflow)
then the concentration of O2 in the water will decrease. In your case
the aeration is probably great enough such that the plants can't quite
produce O2 fast enough. I wouldn't worry about it unless your CO2 level
is too low or you are worried about your CO2 expenditure. What are
(usually) your CO2 levels (am and pm) and average bubbles per second?


ON a related topic...
I have thought about the concept of a general rule of thumb for CO2
bubbles per second compared to CO2 levels etcetera... what do the more
experienced aquatic gardeners think of it (see below)?
If you average less than 1 bubble per second per 70 gallons of water and
maintain "the optimum" CO2 level in your tank then you probably have a
very low air/water interface rate and run the risk (with medium density
planting and fish load) of running out of O2 overnight and should
consider increasing this interface (e.g. spray bar more elevated,
surface agitation, water flow near the surface, air pump on a timer,
whatever). If you have over 1 bubbles per second per 30 gallons then you
should be very safe, even under high bioload. If you have over 1 bubble
per second per 20 gallons then you can safely reduce your surface
agitation (and save on CO2) or fix your reactor!
Of course this all depends on size of bubble, how efficient your reactor
is, bioload, air pressure (height above sea level) and probably several
other factors... but would it be a reasonable rule of thumb? Do many
people use less than 1 bubble per second per 60 gallons successfully
(with fish)? I haven't thought out the exact details of the numbers.




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