Sorry For Bein A N00b But Whats Substrate?
The bottom of the tank. So no substrate = bare glass. Substrate options include sand, gravel, peat, and a variety of other things depending on the fish being kept.
§tudz, geo7x, inchworm -- interesting thread. My gut feeling is that not all Corydoras need the same thing in terms of breeding conditions, so being too proscriptive about things is perhaps counterproductive. My baby peppered cats seem to be thriving in sand and mulm, and because of the stuff in this tank, I didn't need to provide any food for several days after they were free swimming (and I'm not entirely sure that even now they aren't mostly eating algae and the tiny pond animals in the mulm). But they're growing very well, and without any apparent losses. On the other hand, with more delicate species, there may well be reasons to keep the tank spotlessly clean, particularly those from soft water environments. By analogy with halfbeaks, when you take fish from zero hardness rivers and put them in regular tanks with measureable hardness, those fish get bombarded with bacteria for which they have no resistance. So cories from soft water places, especially as newborn kittens, may be intrinsically more resistant than ones from harder waters (like peppers). But those species that don't mind the bacteria may actually benefit from a "dirty" tank in the sense of having a diverse and constant food supply, especially during the early days.
Cheers,
Neale