Hopefully even though it will be very disruptive to the whole tanks ecology it won’t cause a full crash or restart the whole cycle.
I doubt it'll cause a full blown crash, and I doubt the transition will be flawless either. You'll probably get a mini blip which will correct itself quite quickly.
If you squeeze all that gunk out and let your new filter suck it in, and then, for good measure throw the old battered sponge in your tank too, just so you're not wasting those bacteria which are actually attached to the sponge, and not just the crud within it, then I think you'd be in with a good shout.
And don't feed for a day or two, the last thing you need is a continued production of ammonia with a slightly decreased number in BB.
Be sure to post some pics when it's all settled down.


