Lima minor, or duckweed as it is better known, grows on ponds and still waters world-wide. It is a very undemanding floating plant consisting of nominally four leaves approximately 4mm long with a short root underneath in the centre. The plant's leafs are glossy green on top and a lighter matt green on the underside.

The plant propagates rapidly by division, so much so that a few single specimens will quickly take over the aquarium, reducing the light available to other plants. Properly controlled however, duckweed is an ideal canopy to prevent fish from jumping whilst providing a haven for fry. It also acts as a great base for Gouramis on which to build a bubble nest and also provides shade for fish that prefer more subdued conditions.

At one time I used duckweed almost as nitrate reducer. I grew it in one aquarium, then I would scoop off a couple of net fulls each week and transfer it to a different aquarium for a plec to eat. Plants use nitrate to grow so effectively, I was removing nitrate via the newly propagated plants to use in another tank as food.

Although propagating duckweed is regarded as a sign of good water quality, since a single piece of duck weed spreads so quickly, this lovely little plant is often classed as a pest.

The simplest method of controlling duckweed is to scoop out every single piece with a net however, I have found that inevitably, one will miss a bit or leave some on the net and soon the surface is riddled with the plant once again.

I'm not a great fan of adding chemicals to an aquarium but commercial products are available to control duckweed. Accidentally, I found that Methylene Blue also kills duckweed but its detrimental effects on filter bacteria and other plants limit its use.

The best method to curb the plant's spread is to introduce fish that are herbivores. As mentioned, the Common Sailfin Plec (Glyptogolichithys gibbiceps), will feast on duckweed but other alternatives are, Silver Dollars, Distichodus sexfasciatus or many of the African Lake Cichlids.