[BlueAbyss]

Are you sure your test kit is accurate? I would cross-check with a different test kit to be sure first, since everything looks good (leathers do stuff like that once in a while, oftentimes culminating in a 'shed'... better move stuff away from it so the shed mucous doesn't fall on something and kill it).

Snails and shrimps are generally really sensitive to nitrite, so if they are still active and look normal I would assume that all is relatively well (except the test kit). Definitely check with a different kit to be sure.