I cannot agree with this more. PRIME is awesome and has saved my butt more times than I care to remember. Worth its weight in gold. And pick up a test kit. Have you possibly used tap water while cleaning your filter media? If so, you killed off your beneficial bacteria colony. But really, a test kit will give you all the answers you need.Do you add a dechlor/chlroamine remover like PRime? I would actually suggest dosing with prime right now, it will help if it's a nitrite or an ammonia issue.