My tank is slimy and grey - Nitrates high please help :(

Hi! I've been struggling with a slimy gray substance in my tank for a while. My water parameters have been normal, so I’ve been managing it with regular water changes. However, two days ago, I did a 50% water change, deep-cleaned the filter, and removed a buildup of brown sludge from the filter medium. I rinsed everything with dechlorinated water, and the filter was flowing normally afterward.

But in the past 48 hours, the issue has gotten much worse. The slime has completely taken over the filter, turning white instead of brown. The filter is now so clogged it barely works, the water is cloudy, slime is building up on the tank walls, and my nitrate levels have spiked.

I’ve temporarily tubbed my fish, but I need help figuring out what to do next. Did I crash my cycle? Do I need to restart it entirely? Should I keep him tubbed until the nitrate levels return to normal? How can I clear out this slime, and what is it?

Any advice would be greatly appreciated—thank you so much!