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[APD] CO2, water changes and pearling vol 2

Water change treatments:

Large water changes can be done without exposure to air, flow
through water changes, drain and fill at the same time and run
extra time to account for any mixing of fill/drain water.

I chose different locations of Java fern show this to be the

Java fern high up will pearl and the lower fern often will not
and certainly will not pearl to the same degree.
One might suggest that the lighting gradient in the upper part
of the tank is the factor there. More light= more
photosynthesis/higher growth rate= more O2 production.

If so and if you accept that to be the case, that opens up an
interesting little test one can do.

Do the large water change, and observe the lighting gradient.

If the degas hypothesis holds true, you will see even placement
of the bubbles.

If the bubbles are really true pearling, you will see a gradient
of pearling from high to low proportional the light intensity.
This is simple, most aquarist can test it __without__ a DO

It is a reasonable conclusion as well.
Degassing has no role in pearling and photosynthesis growth
rates, light does.

So we should see degassed random bubbles everywhere, not in any
pattern. But that is not what was observed many times. I have
not seen this for many years and have never bought into that
hypothesis of degassing water. 

So I tested it and it is wrong, at least with this tap water and
every tap I've ever used as well as barrel aged(week) RO etc.

So why else might we see dramatic pearling at the upper level 
but not the lower level?

Exposure to air.

That allows lots of CO2 to come into contact with the plant.
Ferns use only CO2.

Large water changes are easy to do and see the effect.
Likewise, you can do smaller water changes or gradiations in
between and see patterns, and also do flow through fill/refill
water changes that avoid air exposure. These also shows little
in any pearling after such water changes. This can be measured
via a DO meters as well, no difference(5% or less in the two I
just did). 

The intense pearling after a water change often shows us what
plant's true potential really is, even if temporary, it'll also
show the need for more work with CO2 and delivery options to
maximize non limiting CO2 levels for plant growth.

So we can do water changes in the early morning right as the
lights come on. then the next following day repeat and so forth.
You can measure the uptake of NO3 or PO4 etc and see an increase
in uptake rates also. 

It would be nice to run a week's worth of daily air exposed
plants(you could reuse the same water) and measure O2 levels,
NO3 and PO4 uptake.
The tank would look awesome at the end of that.
Then we can limit things like light more effectively to mange
growth rates.

This idea might also be a good reason why water changes and air
exposure with non CO2 tanks also can cause issues.

You can also do a simple test with the light gradient:
Place a dark piece of material to block all the light and see
the gradation from high to low light and you will also see the
pearling gradation as well after the water refill.

Distance from the light source works pretty well though.
It can show whether or not the pearling is due to photosynthesis
vs CO2.  You can use the same drained water for a refill if you
want to rule out new tap water NO3/PO4 differences from, the
tank water's NO3/PO4 levels etc also.

Just remove the tank's water, exposure the plants to air for 5,
15, or 30 minutes etc, spray or splash with water to prevent
dessication and refill with the same water.

Simple enough.
Look at the pearling differences.

Then think about how you can improve the CO2 delivery now that
you have a CO2 maximum standard. I think CO2 mist does this to
some degree. It also provides a good reason to do large water
changes for general CO2 related problems. If the plant pearl
well afterwards, you know it's likely CO2. 

The degassing theory is long gone as far as I am concerned with
some rather simple testing that most any aquarist can do.

Tom Barr


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