Duck weed or no duck weed

Traditionally, we were all taught to hate duck weed. It did not belong in the aquarium, supposedly. Recently Matt Owens' book, The Alternative Aquarium: A Robust Habitat changed my mind, and since then I've been studying a Dutch site on ecological aquarium keeping as well. And the more you start researching Duck weed online it gets positively interesting.

Duck weed hoovers up ammonia, nitrites and nitrates, and it oxygenates the water - and then to think people did not use to like this plant. There are many interesting posts and articles to be found:

• http://www.guppies.com/forums/showthread.php/18686-Duckweed-and-waterquality-a-blessing-in-disguise
• http://www.planetcatfish.com/forum/viewtopic.php?t=26791
• http://www.mobot.org/jwcross/duckweed/duckweed.htm

It makes me wonder, how did I ever get by without it? The general principle seems to be that plants under water do not get but so much CO2, whereas plants that grow out of the water, or in this case, that float on top of the water, can absorb CO2 from the air, and therefore can grow much faster, and in the process absorb the fish wastes, which are nutrients to them.

Besides all of the wonders of sucking up nutrients at a fast rate, there is also the fact that it slows down evaporation, and therefore it is an alternative to a canopy, if you want to have an open tank...

As my new 29 gallon tank matured, and ammonia and nitrite finally went to zero, initially my nitrates were as high as 40 ppm, or even higher, upto 80 ppm at times, but duckweed was well... growing like a weed, and while I recently did a partial water change, I also just harvested some duckweed to see if it will indeed end up lowering the nitrate level, for my tank is fairly thinly populated, with just 5 amano shrimp (I think - though I started with 6...), and 5 pygmy cories. In the end however, with Duck weed (and Hornwort, and other plants), my nitrate reading is typically in the 5-10 PPM range, without water changes.

Here are some recent pictures:

4/28, with Duck Weed cover...

5/4 with the hidden LED to penetrate the cover

and some of the occupants:

5/4 pregnant Amano shrimp walking out of the picture

Ok, so I gave up trying to catch one of them in the picture, but there are three pregnant females... of the original three males I recently can find only two, so maybe one gave up the ghost during my two month tank cycling period, which seemed to go very slow at times.

Be that as it may, they do seem to be thriving, and my five Pygmy Cories, who don't pose well for pictures either, seem to be doing very well also.

The biggest challenge with the Duck Weed has been the lighting, for it not only slows evaporation, it also shields the light.

Duck weed and lighting

I was getting concerned with the weakness of the light, and it seemed evident to me that the plants needed more. 

The lighting has evolved to:

• Hagen Flora Glo, which has the right color temperature for plant growth (2,700K). but low output (650 lumen/90 LUX). At some point, I may consider replacing this with a Life Glo Bulb, which has higher output (1,470 lumen, at 6,700K).
• A Deep Blue Micro 3W LED SolarFlare, which gives the Wisteria some needed light. Color temperature is 6,700K daylight. 
• A Marineland 21"Hidden LED that clamps to the tank frame inside the lid, and penetrates better through the duck weed, being right above the water line. It has 72 LEDs, with Par/Lux at 12" 25/1121 and at 24" 11/377, with 550 lumens, and the color temperature is 6,500K, which is daylight.

This is still not high intensity lighting you would need for serious plant growth, but with fairly regular, low light plants, it will definitely do. All in all it is a modest, but workable solution. The Wisteria is growing by leaps and bounds, and soon I'll be donating plants to the pet store... Two Amazon Swords produced three offshoots, which are catching on. The problem area is the excess shade below the massive Wisteria, so I will have to start pruning, which should help water quality again by stimulating growth... talking about which... the last few days I seem to have stabilized at pH 7.0 and ORP 85, with an rH in the 22-23 range, which should be excellent, except I still have no objective way to measure if there's actually any Hydrogen present in the water, though it might be the case by reason of the Wonder shells, especially because of the Magnesium.