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