# Is there a crowding effect?



## HeyPK (Jan 23, 2004)

I know that there are some aquarium plants that can grow happily under crowded conditions, such as _Najas, Vallisneria, Hemianthus micranthemoides or H. polysperma._ but there are others which I suspect need lots of room and open water in order to be healthy. When crowded, they just don't respond well to nutrients, CO2, and lots of light. With EI fertilizing, intense CF lighting and regulated CO2 dosing, it is hard to imagine that lack of nutrients, CO2, or light is limiting growth, but I think something is.

Or am I just imagining things and the plants are really deficient in something?


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## Cliff Mayes (Jan 29, 2007)

I think all plants are crowded and it doesn't stop mine from growing faster than I like.

Every time I plan a tank with just one or two species I always end up with five or six. When I try to keep the Riccia, Java Moss, Duckweed etc. seperate, the sparse looking tank gets the excess.
The only tank with few species is a Shrimp tank with lots of Java Moss. There is some Riccia in there and a couple of others that I can't get to. I do not want to mess around too much cause I think I gave the LFS an expensive loach with the last batch of Moss. Giving plants some room never seems to work out.

Look for some kind of deficiency. It is probable that some of the exotics that we keep would enjoy more room but I have not been able to pinpoint it. Probably some of the specialists can offer some info. Whenever I see plants in the wild they alwys seem to be jammed together.


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## BryceM (Nov 6, 2005)

Hmmmm. I'm guessing what you're seeing is a result of too much plant mass for a given amount of light. The light that strikes directly from the bulbs is only part of the story. There is a lot of scatter and internal reflection that gets soaked up pretty quickly by a dense plant mass. Lower leaves end up getting shorted. Plants that put on lots of mass in the upper regions of the tank cast a huge shadow too.


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## Minsc (May 7, 2006)

I believe overcrowding can reduce a plants access to CO2, and can adversely affect more delicate plants.
I've seen many Ludwigias, Rotalas and Toninas either badly stunt or start to rot when access to circulation was reduced, typically because of overcrowding as the plants grew in.

For example, I recently replanted some Tonina 'belem' rather densely. Within a week, all the stems that were tucked away from the direct current of the tank died. All the stems that were in the direct current remain perfectly healthy. All the stems were receiving the same amount of light.
Previously, I have had extremely dense stands of this plant remain healthy in the highest flow areas of my tank. 

Ever since I started placing plants in the tank according to their robustness, I have had much better luck. Rotalas where they get slammed with current, Limnophila and Hygrophila in the dead zones where nothing else will be happy


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## Zapins (Jul 28, 2004)

Might also be allelopathy . I hate to throw that card down as the most likely explanation, but it might have some influence on growth if you think about it. 

Less water circulation = allelopathic chemicals would stay in the same vicinity for longer making their effects more noticeable. 

But crowding also limits the nutrients/light etc... as everyone else said. I like my exotic explanation better though xD


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