Hi all,
Yes, the leaves of "Indian Almond" (
Terminalia catappa) produce both tannins and DOC, this has the effects of tinting the waters, lowering the pH (but only in systems with very low dKH) and providing some anti-microbial activity. There is scientific, as well as anecdotal, evidence to support this: "
ANTIPARASITIC, ANTIBACTERIAL, AND ANTIFUNGAL ACTIVITIES DERIVED FROM A TERMINALIA CATAPPA SOLUTION AGAINST SOME TILAPIA (OREOCHROMIS NILOTICUS) PATHOGENS" <
http://www.actahort.org/books/678/678_25.htm>.
There has recently been a review paper published "
Herbal biomedicines: a new opportunity for aquaculture
industry", <
http://www.springerlink.com/content/tv4284j427251t68/fulltext.pdf>, which reviews a lot of different plant material (mainly as diet supplements for shrimps). This shows that a wide range of plants from a lot of differing families show some beneficial effects. Bearing this in mind it is quite likely that a lot of plants we can find in the UK will have similar properties to Indian Almond. As Tom says Oak leaves and Alder cones have some history of use in the UK and definitely work. Other leaves I've tried include Evergreen and Deciduous Magnolia and Oak, Loquat, Guava, Blueberry, Camellia, Beech, Hornbeam and Birch. I've also tried Oak and
Robinia bark and all of these have proved non-toxic, with some tinting the water fairly heavily (particularly Oak bark & Alder cones), and others having little effect on water colour. What I haven't done yet is had a more scientific look at their relative abilities as anti-microbials and acidifiers.
My CRS do not want to know anything about catappa leaves. It was advertised that CRS eat them, but they do not. I can not say for other shrimp anything on this regard.
I think that all shrimps will graze on the leaf surface, once the leaf has been in the tank for a while and started to decompose and a biofilm develop. If you collect fallen deciduous magnolia leaves
M x soulangeana) you will find that the shrimps will reduce them to skeletons fairly quickly, but if you use more resistant evergreen leaves like
Magnolia grandiflora,
Camellia x williamsii or Eriobotrya japonica, the leaves last much longer. I was recently asked about evergreen Magnolia leaves on another forum <
http://www.plecoplanet.com/forum/showthread.php?t=13097>, because some-one had seen this video <
http://www.youtube.com/watch?v=OuCkV_c2bC4>, but I think this is a more informative link <
http://www.petshrimp.com/discussions/viewtopic.php?f=2&t=1711>. Magnolia leaves are also widely used by Dart Frog enthusiasts, so I think they should be all right.
Cheers Darrel