Comparing N:P ratios and critical cocnetrations in aquatic plants, algae

Tom Barr

Staff member
Jan 23, 2005
Some more on this topic:

"Ranges of concentrations of elements in water, sediments, and plant materials from the examined lakes are presented in Table 1, Table 2 and Table 3. ANOVA indicated that water, sediments, and plant materials (for each species separately) of all the sampling sites differed significantly in terms of the contents of the examined elements."

When sampling aquatic plants and their growth, we do not measure just the water column, which is all most aquarists ever bother with.

We measure:


Add ADA AS or use mud like in a classic non CO2 tank etc.
How does this influence the plants and the availability or limiting values for algae and the plants?

From Samecka-Cymerman and A. J. Kempers, 2003 Ecotoxicology and Environmental Safety Volume 59, Issue 1 2003:

"Because the ecological and physiological optima for overall plant growth in aquatic environments is about 200–400 μg exchangeable P per gram of sediment (Carr and Chambers, 1998), the phosphorus content in the investigated lake sediments did not limit the growth of the hydrophytes we examined."

This means you cannot discuss the plant's limitations, rates of growth, water column impacts alone.

You cannot do this, yet many aquarists seem very willing to throw basic logic out the door and claim that their limiting water column nutrients somehow prove that plants can grow in nutrient poor waters, the water column might be limiting, but the entire system, with the elements that the aquarists often over look, are far from limiting.

While I understand and see this, many aquarist, for some reasons, wish to argue in favor of supper lean water column dosing, and know virtually nothing about sediments.

It's mind boogling to tell the truth.
When I point this out, they ignore it or use "there are many things we do not yet know or have yet to discover about growing aquatic plants" or some other general baloney statement you'd expect to hear from a used car salesman.

Bull manure.

I suggest less nutrient dosing using EI using ADA As with this in mind, however, adding full EI does no harm either.

However, you can still get great results(non limiting growth) with 25 to 50% EI using ADA AS. Plants are still not limited.

There's been a great deal of nutrient-centric focus in the hobby, but much less with respect to CO2.

There is less sediment CO2 sources however, and most comes from the water column.

Critical review of one's CO2 content is much wiser.
It also yields the best, most predictable and helpful results.
Light is also the last factor, but it's virtually never tested in this hobby.
Adding to the issues are folks that do not bother to do any back ground research, look for methods to test such hypothesis in their tanks.

If have 3 things you should measure to reach a good conclusion, and you only measure one, you really cannot say much.

A good test is to use an inert sediment like silica sand, then dose the water column. Another way to test the sediment only if to run a flow through for the water above to continuously exchange it. Plant tissues? Well, you have send off for that or learn how.

Still, you'd think folks would realize that sediments can play a role and that their use is not bad.

ADA folks are often so blinded, they miss the obvious test and things, many just do not care, but curiously like to tell folks that you must do this or that to have success without ever having tested it.

You cannot say much of anything about the parts if all you do is a large combined thing.

You can say ADA system as a whole produces nice plant growth.
But that's about all.

You cannot say what in particular causes the results.

Tom Barr


Junior Poster
May 21, 2008
So this would mean that for plants, we need N:p ratio to be 1:1?
How this aplies to EI method?