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[APD] Pearling after water changes, some experimental observations vol 1

Many suggets that the pearling we often see after a water change
is due to air/O2 and other gases such as N sticking to plants
and is not true O2 pearling.

There are a few ways to address this to see if it is in fact
"increased growth" or just sticky bubbles (This arguement has
merit and must be addressed and ruled out/accepted).

One way to test and see is:

I recently tried something interesting with hair grass.
I took replacement water that was at equilbirum with air and
tank temp.
So no air/gas, etc is going to come out of solution and stick to
Sound reasonable? There's no high CO2 etc from the tap water
here, the buckets full of water have been sitting for a week and
the tank and room temps are equal. Note, the replacement water
is RO, no other nutrients are present such as PO4 which can
increase pearling in less than 40 minutes if the tank is

I drained the water down to exposure the hair grass to the air.
I slowly refilled the tank with the low CO2 warm water.

Observation #1:
The plants had no bubbles upon filling the tank.

Observation #2:
After 15-30 minutes, the plants began intense pearling, very

As intense as you could possibly imagine and I've ever seen.
Anyone could tell and see this massive difference.

Nutrient limitation is ruled out due to EI and ADA aqua soil(4
months old). Light is at 300 micro mol, plenty high for good
photosynthesis. Plant health is good.
No fish, no snails to speak of.

Why would the plants not have bubbles after the water change,
then formation occurs 15-30 minutes later?
The water is at equilibrium so no degassing is going to occur.
The only reason I can figure out to such a degree that
influences plant growth like this is due to exposure to air for
5 minutes.

What is in air that's not at high levels in the tank that would
induce intense growth?
CO2 in the gas phase.

This shows/strongly suggest that aquatic plants can dramatically
increase production and growth if they are supplied with a gas
phase of CO2.

It's a simple test and the observation #1 shows that it's not
due to degassing tap water etc, it's due to the gas phase
exposure to air.

Mimicing this with CO2 mist is a generalized concept for that

So what about air just leaking out vs O2, the standard for
pearling and aquatic plant growth?????

Experiment no#2:
I have a DO meter that measures O2 levels in water. 
O2 levels are strongly correlated with plant growth and
production in aquatic ecosystems. O2 levels are used to
determine productivity(true pearling) in a quantative manner in
research science.

This allows me to measure the rate of pearling or the rate of
total plant and/or algae growth due to a treatment.

So if I have a tank that's limited due to PO4, then add PO4, I
see dramatic pearling increase and can verify this with my DO
meters as well, often times by about 30-50% growth increases if
the PO4 limitation is fairly strong. So this is a fairly useful
tool used to measure plant growth in our tanks!

Few plant aquarist have these devices, I think only George Booth
was about the only aquatic plant person besides myself on the
web that uses them for aquatic plants.

So I tested the before and after O2 levels at the same time I
did the water change above. I had 7 ppm(100% a tad over) before
and 11ppm after(t= 2 hours) or about 160%.

60% higher O2 is something anyone should be able to "see".
People huff and moan about various things to improve their plant
growth, yet CO2 can increase the growth by 10X easily or 1000%
faster vs ambient in submersed plants when the CO2 is in the
dissolved aqueous.

It is far more critical in terms of growth improvements in most
cases than NO3 or PO4 etc. CO2 is also far more ephemeral than
PO4 or NO3.

Yet few test to see if the water change is really adding a gas
phase of CO2 that increrases the plant growth, instead arguing
it's just degassing water and never really getting to the bottom
of anything.

Talk talk, not test test. 

As far as I know, this is the first demostration without a O2
meter to show and confirm that pearling in this case was due to
gas phase exposure to CO2. The backup with the O2 meter offers
more support for the contention as well.

If folks see intense pearling after a water change, and then for
the remainder of the day(do a large water change early in the
day), it generally means it's due to the tank not getting as
much CO2 to the plants as it could.

CO2 mist side steps adding a lot of CO2 gas into solution,
rather, it leaves it in the gas phase. I've confirmed CO2 mist
increasing the O2 levels by 50% without no change in bubble
rate(contrst that to the 60% in the air exposure experiment!, I
have 10% more to go, well, actually a lot more replicates:( ). I
just simply switched from a mist injection from a reactor with
100% dissolving efficacy(All the CO2 is dissolved).

I'm not happy with the CO2 measurment, so comparing the ppms is
harder to do since the error overlaps between both treatments,
but the bubble rate of CO2 delivered to both treatments remained
the same. Also, the error overlaps, so that CO2 membrane KH
reference idea is going to come in handy for very close precise
measures of CO2. There was a reason why I looked into that.

Once I get good CO2 measurements that I can be very confident
about, then I can move forward and argue very strongly for CO2

Many have already seen the dramatic effects of the mist method.
Many complain there's too much growth and that such pearling is
a distraction.

But others like it and I personally do as it kills off algae as
well and I like to push the limits of systems till they break or
crash. I'm weird that way I suppose 

Tom Barr


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