Cloudy tank is typically a bacterial bloom.
Have you added any carbon sources recently (vodka, sugar, Vit C)? If this is the case keep your eye on the PH and areate as much as you can if it gets low.
My second guess would be a kalk overdose. If this is the case then I'd suggest just sitting tight, turn off any dosers/ca reactors for a day and you should be fine.
Neither instance typically results in a tank crash.
And granular activated carbon will not cause cloudy water. It's actually helps with water clarity.