tannins and plants
 

Do plants use the tannins from DW that are in the water?

The "cycle" through all the water that passes them for nutrition....but not usuing it as in you have tannis stained water and the plants magically clear it up over night (if that's what you were looking for).

I meant are tannins "nutritious" for plants. I read something on another forum that seemed to imply that the tannins are somehow useful to plants. I actually prefer water that's a little stained. Looks more natural to me.

Yea me too! From exp with tanks TOTALLY tannins stained due to DW, leaf litter, peat etc VS the tanks that didn't have all that and more the 'crystal clear' set up but partly the same plants. They did grow better or better say faster then the one's in 'clear' water. Now what makes them thrive better in the brown water and just how much they'd use off of it I can't tell ya....I just know when it works for my fish & plants I leave it at that and don't question it (don't fix something that's not broken lol) :-)

Plenty of people have blackwater tanks that are heavily planted, so I don't think plants will use up tannins to the point of reversing the blackwater effect, if that's what you're asking.

I wouldn't think so. Tannins are found in all plants naturally, and serve to do other things to protect the plant from invaders and such. I have no special knowledge in this, so have a look at this reference which though technical explains how they operate.
Tannin - Wikipedia, the free encyclopedia

My concern with tannin stained water would be the reduction of light intensity that would affect the plants. Other than this, to the best of my knowledge, tannins pose no detrimental effect for fish or plants.

Byron.

I'd not be concerned about that part, the 15 & 20 g's set up I had were like super stained, where the water look pretty much like fresh brewed coffee and even there the plants were thriving (needed this set up for inhabits in these tanks); and as usual that was my usual low light home store florescent with +/-1wpg as always.

Interesting. It doesn't actually say anything in the wikipedia page that makes me think tannins would be detrimental to plants, except that in some cases excessive tannins may inhibit absorption of certain minerals like iron as it is an iron chelating material. I have a feeling, though, that if there was a significant impact of tannins in the water on plants, there would be information on this in plant/aquarium literature and someone would have come across it by now. I will say that the plants in my "tannin-ized" aquarium look a lot happier than the plants in my other clear-water one, but there are several other factors at play so it's hard to deduce anything concrete.

And tannin water is more acidic, and most of our aquarium plants come from soft acidic water and prefer it, so I would expect better growth just because of that fact.

Well like I said my 10 gallon, "coffee-water" (good analogy Angel) has plants that are doing much better than in the clear water tank, but many other factors at play there.

So, bottom line, the tannins themselves don't benefit the plants other than creating a more acidic environment closer to what the plants prefer in their natural environment.

I think there was confusion on the purpose of the question. I had read on another forum that plants will "use" the tannins in the water, but it seems that this is not so.