Hi Will, I have just used in date API master test kit about an hour ago. Given the issues and massive spikes (off the carts) I performed a constant water change of around 300% with dechlorinated (prime) tap water. Readings are now 20ppm nitrate after ferts (tropica complete), Nitrite 0.25, ph 7.4/7.6, ammonia around 1ppm. I had (now moved to 150L tank) betta and 1 Armano. Yes it’s a HOB filer oversized maxed out on cycled media (cintered glass not weighed) from said 150L, white stuff is filter floss 🙂. Tank around a year old, never vacuumed the gravel but create currents with my hand to sweep up the mess (betta removed obviously). I was using purigen but that’s been removed to see i can get the tank to cycle again. I have a good 1.5 inch layer of fine gravel so surface area for bacteria should be fine in addition to media. Can overdosing prime cause a cycle to crash?