I understand that pearling happens because of photosynthesis. In the presence of light, plants consume CO2 and produce O2 that is released. Now my question is, under optimum conditions (light, nutrients, CO2), is pearling a continuous process in a healthy aquarium? I observed strong pearling when I increased the light from 2.4 to 4.6W/G. However the pearling lasted for two days after which it stopped. Now I only see small bubbles underneath the leaves of my plants. No change in light, CO2 etc.

4.6wpg Waaaaaaay too much light. Youll find that the plants were just taking advantage of the suddenly available high light. If youve not upped the CO2 AND nutrients to compensate for the massive light, then the plants wont be able to get enough, leading to deficient growth in whatever runs out first, probably CO2..

Turn the light down, let the plants get used to 2.4wpg with good solid CO2 and EI (this takes some time), theyll be pearling nicely after a few hours of lighting. A good solid stable slower growth, is far better than trying to run the tank at 400 miles per hour, running out of CO2, having massive algae problems, awful looking plants.. but lots of bubbles.

Also bear in mind, some plants dont pearl as much as others do anyway, Riccia is a very good indicator as to how you have things setup. If you see lots of nice little bubbles by 1/2 way through your photoperiod, leave it be.

A wise man once told me.. 'The only things that happen in an aquarium fast, are BAD'

Although I am using 4.6 W/G, the lights are hanging 8" above the tank. I switched to high light because my Rotala rotundifolia, Ludwigia repens, and pearlgrass were not doing well. After increasing the light, I have noticed a considerable difference in their growth and color. I also increased the CO2 from 21ppm to 30 ppm.

We have no way of determining how much CO2 we have to that accuracy. If your using the KH/PH relationship, then you have between about 10-40 ppm. the only way to be sure is to use a drop checker with a KH reference solution.

Thats still a heck alot of light.. its more likely your plants were struggling for other reasons other than light. Nearly all plants will grow at 1/2 that.. its more than often CO2 thats the issue.. test kit methods of measuring are totally pointless due to the inaccuracy and other factors in the tank that can effect PH.

Dose with EI, then all you have to worry about is CO2.. use EI and a drop checker, and youll be amazed.

what is EI?

its a method of nutrient dosing called the Estimative Index. It allows us to provide nutrients in a slight excess, without the need for any test kits, or general messing about. This means that it gives us far far less to worry about.

Have a look at the Estimative Index discussion for details itll change your aquariums life!

So was it due to adding more CO2, or was it due to the increase in lighting?

Why do you think that the pearling and good growth only lasted 2 days?
You ran out of something. It was not light and does not sound like it was CO2 either.

NO3
PO4
K+
Traces
Ca/Mg

See the EI article, it makes adding these very easy and rules out deficiencies as well as excesses in a couple of very simple steps anyone can do and does not require testing or chemistry knowledge.

Tell me the tank size, I'll tell you what to add and how frequently.
Ideally, after a large water change, there is a lot of pearling and you should try and see if you can attain that same growth and pearling all week long.

If it backs off a tad, that's okay, but the tank should pearl good most of week and after 1-4 hours if you use higher light/CO2 etc.

Riccia is a good indicator plant for pearling also.

Regards,
Tom Barr

Tom, thanks for the reply. Well, I have a 10 gallon tank. I use Hagen plant grow fertilizer (5ml/10 gallon) once a week.

Slightly off-topic, however, as Frolicsome_Flora suggested, I should use a drop checker for estimating the CO2 levels. I was thinking of making a DIY drop checker. I hold a PhD in molecular biology and therefore work in a lab where we use ultra-precise intrument and extremely pure chemicals (molecular grade). Now as I understood from some the topics, I have to have a vessel containing NaHCO3 solution in deionized water equivalent of 4dKH. That is 50mg/L NaHCO3. Purity and correct measurement is not my problem. So if 4dKH is 50mg/L, I'll jolly well make this solution. Then I have to add few drops of pH indicator. I could use Bromo thymol blue or Phenol red. And then I have to enclose this solution in a vessel that is made such that the colored solution is in ocntact with aquarium water via a gas phase. Correct me if my understanding is OK.

Thanks.

You can't use Phenol red as an indicator solution and still use 4 dKH water. That KH was chosen to make the solution be at it mid-point on the indicator color chart at 30 ppm of CO2. Phenol red's mid-point is about 7.3 pH, which would require a 20 dKH solution in the bulb to reach the mid-point at 30 ppm of CO2.

And, it is important that the drop checker be entirely submerged in the tank water, to avoid any distillation between the water in the drop checker and the water in the tank.

I think you have the ppm of NaHCO3 wrong also, but I could be mistaken. I think 1 dKH = about 18 ppm of CO3. I admit that I am no chemist, and I get the relationship between ppm of sodium bicarbonate and dKH confused.

Well, if you are molecular person, then it's easy. I just went through the core molecular plant bio grad group here at UC Davis, I got a lot out of it.

You got the idea.
Just take a test tube and bend it in 1/2 making a nice even bend(pack the test tube with sand, this will prevent kinking when you bend it, about 1.5" for the bulb end and 1" for the open end.
10-12mm tubes will work fine.
Add a glob of glass for the suction cup.
Cool and then use.

Use sodium carbonate instead if you have that type of access.
Make a few also, different sizes if you have various test tube sizes available.

With good equipment, you ought to be able to make a 71.440ppm solution of alk pretty easily(carbonate hardness) with a scale and DI water and Na2CO3.
You can make a high concentration, so 40KH, or 714.400ppm.

Make a liter, then dilute by one order of magnitude to make a liter of 4KH.
Add to the bulb(6mls), and then use the Bromo blue, it's precise in the range we want, generally used for 6.0-7.4 pH ranges which is right in the middle of a KH of 4 or 5. You do not have to make a 4KH, you may use 5 or where ever your perception of color is best.

I use the KH solution and then a pH meter as it's accuracy is much better and responsive to pH changes. I use a Dissolved O2 membrane wrapped around the pH probe tip, in place of the KCL electrolyte, I use Na2CO3 electrolyte KH ref solution.

Gas (but not the tank water and KH solution) travels across the DO membrane and then the pH is referenced to the 4 KH reading.
It does not matter if the gas is N2, Ar, CO2 or O2.
Only the CO2 will influence the pH.

There is no phase change time issues this way. That is a hard issue to overcome, it works but the best you might hope for is a 1-2 hour response time with a drop checker. The pH meter is a few minutes.

But drop checkers work on a practical level very well, so I'd certainly suggest you make on. They will be time savers later.
I think 6mls of KH solution in the test tube drop checker, 3 drops of the bromo blue ought to do it.

All this stuff is cheap and easy for you to DIY at the lab.

Back to the original question:

Many folks will state that pearling is due to when the saturation values of O2 are above 100%, this is not true.

It's only when the rate of dissolution of O2 produced from the plant's growth is exceed by the production of O2 due from plant growth. Then gas phase forms and builds up into bubbles released from the plant leaves.

Growth is generally defined as an irreversible acquisition of carbon, and photosynthesis can be measured via the amount of O2 dissolved into solution(even if it's well over 100% which is often the case with aquatic macrophytes/microalgae blooms etc).
So as carbon is fixed, O2 is released via our old photosynthesis equation:

6H2O + CO2 and some light/enzymes => 6O2 + C6H12O6

So O2 correlates very well with growth(sugar production via photosynthesis) in practical terms and theoretical.

But when plant growth is good, and O2 levels are low, you can easily have pearling without being near 100% saturation levels with the air. Pearling just means the rate of O2, or growth, is fast enough to make bubbles of O2 that we can see. If that rate is fast, it will not matter that much what the saturation level of O2 is in the tank, O2 is not that souble compared to other gases like CO2 which is very soluble in water.

So pearling is a sign of strong growth, watch for it carefully.
Some folks down play it, thinking bubbles come from other sources, there is some debate about that, but after doing it awhile, you can discern between growth and just funny bubbles, anyone with a decent eye can see the differences.

If you use an O2 meter, the main device we use to measure productivity in aquatic submersed systems, then you can show this in aquariums as well, this gets around the other gas argument easily and quantifies submersed growth.

By doing a bottle test(it has a few issues, so take with a grain of salt), you can get the dark respiration rates also. Instead of suspending a pair of test bottles(one wrapped in 2 layers of foil) in the water, we use a jar covered with foil and another open to the light and place a DO meter inside this with a grommet.

This jar is open at one end and we push in around the plant bed and do the same with a foil covered jar close by.

Gross O2 (light bottle) - the Respiration (dark bottle) = primary production rates.

One thing that has not been done, is this type of test in aquariums over a wide range. Most only measure gross O2.

The DO meter allows you to measure in real time continuously the changes in both the production and respiration of the system.

Most test tend to use test kits rather than DO meters and only measure a before and after reading of a specified amount of time. The rate of growth can decline due to the treatment with the jar, nutrient limitations, CO2 limitation is a big one etc.

We can get around this by doing it and measuring CO2 closely (the other nutrients are not likely to be depleted in a few hours except CO2) at the same time.

We can also do shorter time frames and measure with more precision using a DO meter and the CO2/KH ref methods.

That's where I'm going hopefully later.
I know some folks tank';s are over loaded with fish and their respiration rates are very high, whereas some folk's rates are very low. No one has really done much here with respect to this in aquariums.

I have the equipment, methods and know how to do this
Oh, the important one, the willingness to do it!
The biggest issue of them all.

Regards,
Tom Barr












Regards,
Tom Barr