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).

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 anything.
Sound reasonable? There's no high CO2 etc from the tap water here, the buckets full of water have been sitting for 48 hours and the tank and room temps are equal. Note, the replacement water is RO, no other nutrients are present.

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 intense.
As intense as you could possibly imagine.
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 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?
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 theory.



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 old George Booth was about the only 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 plant growth is something anyone should be able to "see".
People huff and moan about various things to improve their plant growth, yet CO2can increase the growth by 10X easily or 1000% faster.

It is far more critical in most cases than NO3 or PO4 etc.

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.

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. Simply switching from a mist injection from a reactor with 100% dissolving efficiecy(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.

Once I get good CO2 measurements that I can be very confident about, then I can move forward and argue very strongly for CO2 mist.
Many have already seen the dramatic effects of the mist method.
Many complain there's too much growth and that such pearling is a disstraction.

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

Regards,
Tom Barr

Nice writeup Tom. I must admit, I've often wondered about the gas bubble theory also. I get intense pearling after a water change, especially from some Riccia remants (annoying pest) that I am still cleaning up after experimenting with it as a foreground plant. I don't take water straight from the tap. My water is taken from a 30 gallon storage container for natural dechloration (our supply only uses chlorine, and very little of it). Our local water is mostly from rainwater runoff and snowmelt, so it's very low in TDS, so there is not much in the way of nutrients added to the water. I see the same thing that you have described in experiment 1. I get the most intense pearling for about 6 - 8 hours after the change.

Prior to getting pressurized CO2, I used to only have pearling after a water change (I had DIY CO2). Now, with pressurized, and using your misting method (diffuser arranged under the outlet of my canister), I get significant pearling after 2 - 3 hours of lighting, every day, but never as good as after the water change.

This assumes that during a water change, plants are exposed to air.

What about plants below the water line? They are not exposed to gas phase CO2, but seem to pearl more after a water change regardless.

Why not repeat experiment #1, draining the tank to just above the hairgrass, thereby not exposing the plants to air.

If the theory holds, there should be no increase in pearling.

This topic really interests me because of odd observations made on my tank recently. As i posted previously, to combat murky water, I've been injecting air into my system at night. A couple of days ago, I upped the air from 1 bubble every 3 seconds to 2-3 bubbles per second.

At 8:00 am the next day, before the lights came on, and before the CO2 came on, the plants were already pearling like mad. It was not just sticky air bubbles coming through from the air pump. I could see streams of bubbles coming from the plants. This was without light, so there should have been no photosynthesis. There must have been CO2 gas in the water just from the air pump, but how can plants produce O2 without light? I can reproduce this effect very easily just by adjusting the amount of air injected into the system at night.

Makes me think that there may be more to pearling than just photosynthesis.

I've done that Joe, but have left that out, forgetful I suppose:-)...... good point.
Now I think about it, it does not pearl nearly as much (although there is a good amount of pearling still).

This seems to give credence to the idea that exposure by gas phase will give you an increase in pearling/O2.

But a temporary spike of CO2 vs a continous observation like with mist seems to be the real question. You can easily get a nice pulse of growth, but be unable to maintain this same growth rate/momentum later.

If we do back to back water changes each day:
Say 60% one day and then observe, then repeat again at 60% and observe, we can likely make some more conclusions.

We can rule out weekly organic build up(we can also add purigen or Activated carbon etc and this also improves growth is many cases).
This needs ruled out as well.
Converting more of the nutrients to the inorganic phase may help increase pearling.

But the real issue is how long can that intense pearling occur?
Every day for a week or two?

What is it about a water change that causes that intense pearling?
Is it really the degassing water?

I do not think so really, in some cases perhaps.
We can blast CO2 for an hour at high levels and notsee the same effect.
So CO2 alone cannot account for it entirely it seems.

As far as night time, well, there's a lot of bacteria, and murky water really shouts out high loading, wood, so so plant growth here and there, so so CO2, the pearling is likely due to respoiration by bactera, that normally consumed the O2, reducing the O2 in the tank.

Water changes = more CO2/less organic loading.

More organic loading: more bacterial consumption of the organic matter=> less O2levels in the tank= more murky looking water.

Large water changes and more CO2 ought to correct and improve things for you.
You can also try purigen or AC.
Regards,
Tom Barr

First off I should state that I haven't done any specific experimentation just general observations over the last year or so of water changes...

I have a non CO2 tank and after a 50% water change (straight from the tap, not letting it degass) I get water bubbles everywhere, but they pop once and are gone. So in my mind they are not pearling.

Any plants that were exposed to air, have a tendency to produce bubble, pop, and produce more, which I take to be pearling. I've also observed that the longer the exposure to air the more the likelihood of pearling.

I also get pearling after the waterchange on my vallis when I have accidentally 'torn' one of the leaves. I get a mixed feeling from this - 'oh bugger I tore the plant ' and 'cool, loads of bubbles '

First of all, greetings everyone, I`m a new member, but is never to late...

In my case, pearling is much more intensive, after water change, but my TAP water has pH 7.5-7.6, kH readings are about 6, so i have to tnink, that my tap water has poor CO2 levels.

I use PMDD, with some PO4, K2so4, KNO3, MgSO4 x 7H2O, and trace elements, so i think that nutrients are not problem for better pearling.

In my aquarium i have pressurized CO2 sistem, DIY reaktor with powerhead and i have pushed CO2 to about 40mg/l, light is 2x MH 150W for some 350 litres, but i have much better pearling after water change. I think that CO2 is not limit in my aquarium, or my calculations are not correct, or plant can collect carbon better from tap water?

Great site...Keep up the good work !!!

I do have to add that after pruning my anacharis i do see massive amounts of bubbles escaping from the cut stem. I don't see how this can be pearling. Could the pearling you see after a water change be the same bubbles i see escaping from a cut stem, either do to the change in pressure from the changing water level(like on a plane when your ears pop from expanding/contracting gasses) or from damaged tissue from excessive movement from the water change?


Just a thought.

Here are some notes:

I tend several client tanks every week.
One is a larger tank, with high light, 28" deep.

The upper part has Java fern. Lower parts, other species that are much faster growing, thus more likely to pearl.

After the water change, there is no pearling in the first few minutes.
Then, without fail, the places with the highest light intensity begin to pearl first(10-20 minutes after the water change).

This pattern is consistent.
The faster growing Rotala does not pearl and is not close to the higher lighting.

Thus one might think this suggest that the Photosynthesis, driven by higher light=> pearling, rather than excess air accumulation, or sticky degassing bubbles.

My experineces with degassing bubbles contends that they appear almost immediately after the water change, and they stick to everything/everywhere in the tank regardless of lighting......that is if you accept that they are degassing bubbles, which clearly in the Java fern/Rotala case, I do not see how they possibly could be.

This observation and rational suggest that it is not degassing, it is light driven photosynthesis.

Degassing bubbles should stick to everything regardless of location and orientation.

But this is not observed in this tank or my other tanks.
Also, one can do daily water changes and see this same effect repeated every day and a higher growth rate.

The other way is to run an O2 meter and measure the Oxygen, which is higher on water change days but you could argue that the bacteria drain more as the organic matter accumulates through the water etc(adding AC or Purigen etc could act as a control and remove that fraction though).

So it's not just what is in the water, it's also exposure to the air itself.
If it was merely excess gas taken into the plants, you also would not see localized pearling relatable to the lighting.

It offers up more proof towards my contentions about water changes and adding CO2 via gas phases.
I know it's not sticky air bubbles and degassing water in the above cases.
I know what I am seeing along a lighting gradinet is photosynthesis.

I saw that pearling along the lighting gradient(light and pearling are proportional) and knew right away what it meant.
It answers the question in these tanks about water changes, exposure to air etc.

I can also drain and fill at the same time and thus change almost all the tank water with no exposure to air also........so that would give me a tank with a large water change and no decline in the water level, and see if the same patterns exist.

That's next.


Regards,
Tom Barr

The reason I started using a mixing barrel is because after water changes the pearling was so fizzy, it caused certain stem plants to uproot. It was really annoying. Now I mix my change water for two days with a very large powerhead. I still get more pearling after a water change but nothing like when it was straight out the tap. I know for a fact my tapwater has 15ppm CO2.

Too much pearling ?
I reduce my light if I want less growth.
I've recalled with some substrates or shallow depth, that plants would not stay down. Riccia often would pull loose after the water changes if not well trimmed etc.

I think the exposure to air in the non CO2 planted tank is part of the issue about why it might be bad every week or two etc. And in some cases, much less of an issue if the tap have low CO2/you allow the water to sit over night etc prior to changing the water.

We have sonme serious issues in evaluating tap water changes due to the many variables Tap water has.

Some has high Copper
Some has high CO2, some low CO2
Some folks use cold tap
Some have PO4 sometime of the year
Some have varying conditions in the tank

Hard to say as folks seldom test their tap water every time they do a water change




Regards,
Tom Barr