nic,
for discus and apisto there are no plants in their "proper" biotopes...
its mainly drift wood and rotting leaves for the acidity with sand beds.
they generally come from blackwaters.
having said that low-light plants will do well from the tainted colour.
but i remember reading in a thread about some PH lowering blackwater product that doesn't taint the water.
not sure about corydoras.
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