First time tank owner, in theory my daughter's :).
We currently have 250Mg/l of Nitrates, if I read our tester right. This seems extremely high. We have a 78 litre tank, and introduced fish 3 weeks ago (6 Dorios, 2 small Corys, 2 platys, 3 harlequins).
Our Ammonia level peaked at 3-4, and is...