How to do a controlled test for aquatic plants and algae

This controlled test concept has stymied the hobbyists and the various makers and vendors of aquatic plant products for many years.

The main problem is that they had, many still have issues maintaining control over their independent varaiables while investigating the depend variable.

While you can test 2 or more dependent variables at a time, you first would wise to test them individually prior.

Example:
So how to test say PO4 and see how it impacts plant health and algae presence:

The light needs to be the same.
Easy enough.
CO2 needs to be in a good acceptable non limiting range.
NO3, needs to be in a good non limiting acceptable range(If you look at the V/S graph in the first newsletter, it would be Vmax, same for all the nutrients)
K+, Fe, Mn, Zn, Mo, SO4, Ca/Mg, and so on all need to be at high Vmax or higher levels.

Plants wills till grow and do okay at lower than Vmax levels.........but we assume high levels will not slow growth in those parameters.

These assumptions we build in to our test need to be reasonable.
We have to have some to get anywhere, but we can chose them carefully.

A statement I've seen often: PO4 excess causes algae.
So does it? How might we test this to see? Make all the other nutrients non limiting and then vary the PO4 from 0, 0.1ppm, 0.3ppm, 0.5ppm, 0.8ppm, 1.0ppm, 1.5ppm 2.0ppm etc.

We assume the addition of KH2PO4 is all in bioavailable inorganic form.
We assume that 30ppm of CO2 is non limiting at any light level within a range that will produce net growth, so that takes care of light, CO2 and we do the same for the other nutrients.

We try to maintain the levels for one week runs.
Ideally we would have many tanks set up for each level of PO4.
But we can repeat the test many times also. If the other nutrients become limiting, then we have to start over again.
So this can take some time to do.

If folks have this much control to begin with, they generally have no algae issues and many are unwilling to explore whether adding NH4 causes algae, it's typically a mistake rather on purpose when they induce algae.

But if you want to answer some questions, you need to be able to do this and be willing to see if it works or not.

I'll write more on this later.

Regards,
Tom Barr

 

Re: How to do a controlled test for aquatic plants and algae

You can run from it. but you can't hide.
May as well post doc it. There are worse things you could do

The aquatic environment has many other problems that and variables to contend with not present in the terrestrial system.

There is often very little past research on specific auqatic plant species that we often keep, there are some studies done on fast growing permanent weedy invasive plants.

Regards,
Tom Barr