Plants, water movement and ther sediment from Madsen et al, 2001


Lifetime Charter Member
Lifetime Member
Mar 12, 2009
Not too bad of an article. I skipped over a bit on sediment since we're using a well loaded column anyhow, and tried to pay attention to the mechanical issues and growth forms.

It seems that they're concluding that optimal growth hapens under slow, even current. This is nice to know, but I was more interested to see the modification of growth forms through moderate current. Plants seem very aware of what their leaves are doing; be it interspecies competition or water flow. Based on this study I'm beginning to think that a low, even current at the substrate is ideal, with higher current slightly above to encourage compact growth.

Still, this does not seem to be th exclusive cause of compact growth; I have found for my personal experience that compact growth can happen with low current, under low light. Hopefully when my 48 gal gets filled, I will be able to test a tank out with higher current and lower light. If all goes well I'll have 3-4 tanks with the same dosing method and substrate with various lighting, current and CO2.

Thanks for a link to another good paper, Tom.


Tom Barr

Staff member
Jan 23, 2005
For example, I have Blyxa japonica growing in a lower flow region, and one where there is stronger downwelling current.

There is a huge difference in morphology, rates of growth and appearances.
The higher flow rates suppress growth even though the light is more intense, good CO2/same sediment and water column nutrients. Color is different also.

While light is some of it, I placed the same plant in the same tank over where there is less flow, it reverted back to the form in the other tank.

I like the slower and lower growing less weedy growth.
For some species, the effect of current is very pronounced.

While I have 3500GPH of flow in the 180 Gal tank, it's low pressure even high flow, much like the flows one might find in a moderately flowing 0.5-1 knot stream.

The plants grow really large in that tank.
In the other tank there's a high pressure of flow in one corner and the plants do very well there, but tend to stay small/short. I think higher flows cause the plants to grow more roots and more prostrate along the sediment instead of up/more leaves. They'd just lose the leaves and have them stripped off if they did not modify their growth forms for current.

Most all swords/Crypts and Anubias are river/stream plants, so this is why they have strong roots and storage, not solely because they prefer root uptake. They have little choice as to sediment uptake when the dry season starts also.

Tom Barr


Plant Guru Team
Lifetime Member
Jul 6, 2009
The Netherlands
Nice paper. But what got my attention was this:

"Physiological studies have shown that photosynthetic
rates of freshwater macrophytes are positively
correlated with current velocity at low levels
(0–0.10 m s−1), the range likely to occur within
dense macrophyte beds"

And this:

"In experiments conducted at
concentrations of CO2 and oxygen expected to saturate
photosynthesis and dark respiration, Madsen et
al. (1993) showed that net photosynthesis of eight
freshwater macrophyte species decreased as current
velocity increased from 0.01 to 0.086 m s−1. "

So low flow has positive effects on photosynthesis, even when in situ CO2 measurements between plantbeds show fairly low concentrations.

Or am I missing something?


Guru Class Expert
Mar 5, 2009
dutchy;42656 said:
Nice paper. But what got my attention was this:

So low flow has positive effects on photosynthesis, even when in situ CO2 measurements between plantbeds show fairly low concentrations.

Or am I missing something?

The second paragraph you mention rules out CO2 and O2 as limiting factors to be sure the flow difference is responsible of the modification of growth rate.

The fact that important flow velocities leads to slower growth is well discribed over many books. That's why many manufactures use spray bars to avoid "cutting" flow velocities

Personally, to get a good flow over all of my 60G, I use a high pressure/high velocity output in the right front corner, midtank to near surface, directed tangentially to front glass, bottom tank, left front corner. The intake is put in the back right corner, near bottom. That way, I see a good flow directed from left to right. I can watch the flow when I feed, seeing the flakes migration from left to right.

The left part has a much slower flow and flakes sink vertically to bottom. I added for that a second intake, much slower than main intake, via an Y connection + tap control, in the back left corner, near bottom

Near front glass, where flow is very strong, I only put compact crypts and swords. The only problem is that black brush algae like those high speed outlets


Guru Class Expert
Oct 18, 2009
I use eductors or penductors increase current and avoid ‘laminar’ flow. The velocity is lower but the current is greater, I think that is how it goes.

The object as my Dear Ol’ Dad explained it is to make the aquarium flow as much like a river as possible. It seems to work.