tannins, apparent effect on floating plants

[Ben Rhau]

Hi all,

I seem to notice a correlation between the darkness of the tint in my tank water and the appearance of pale, small, or dying leaves in my Salvinia natans (surface floater). No intended difference in light output at the top, and same water source. In my most recent case, I have some new driftwood I moved from one tank to another. It releases a lot of tannins, and I see the floaters doing worse as the water gets darker. I've observed it in my quarantine tanks, too, when I've added alder cones and catappa leaves. I've added liquid ferts, and it doesn't seem to help.

Has anyone else observed this? Is this a known phenomenon, and what do we think is the mechanism?

Thanks,
Ben

 

[MacZ]

That's somewhat counterintuitive. Humic substances tend to chelate certain micronutrient ions, thus pushing their bioavailability.

pale, small, or dying leaves in my Salvinia natans (surface floater)

Those are signs of nitrogen-deficiancy. I haven't heard of any correlation between humic substances and nitrogen compounds.

 

[Ben Rhau]

I don't understand it either. The two tanks where this is currently happening are the two most heavily stocked with fish. The same plants are thriving in shrimp tanks that have very little nitrogen. Also, dosing with ferts hasn't helped.

Those are signs of nitrogen-deficiancy. I haven't heard of any correlation between humic substances and nitrogen compounds.

I would have assumed the correlation was the other way (improved N uptake).

 

[MacZ]

I would have assumed the correlation was the other way (improved N uptake).

If any, yes, exactly this.

 

[Mazan]

That is strange. I have not noticed anything like that with water lettuce, I usually only see yellow or dying leaves when there are too many floating plants in a tank, and have assumed that is because of too much competition for nitrogen.