So sorry I didn't see all these kind replies! A new pH kit taught me that it wasn't actually my problem, which I now suspect was salt leaching out of a big piece of driftwood. It seems to have settled down now after time and regular water changes. This was my first tank built here and it had to be p...

While I realise that by definition most S American catfish come from areas of lower pH I have a tank with a large piece of driftwood (unknown sp.) that sits at pH8. In it are a school of Rummy-nose Tetras who are bright and healthy, but none of the Corys I have tried have been successful and have be...