StanTheBetta
Fishaholic
In a 21 liter tank a common pleco is going to be way too big. I'm not too familiar with the other variations of plecos so they may be littler but I'd still say go with an otocinclus.Fish Buddy said:At Petsmart Otocinclus go for 1.99, Plecostomus go for 2.49, and Chinese algea eaters go for 1.99. Also Siamese Flying Foxes go for 8.99, but I got mine on sale for 4.49! Corries and other catfish are more expensive. You will have to check at your local fish store (LFS).
I recommend Otocinclus because they do to grow very large and are therefore better at cleaning tight spaces like plastic plant leaves.