If it is the only means of filtration in the tank and you clean it so vigorously, what you could be seeing is a bacterial bloom depending on how many days later it clouds up.
The other thing is that rinsing it so vigorously removes the finer particles that have become part of the mechanical filtration of the sponge.
so it is two fold, you may be damaging/disrupting the biological aspects of the sponge (BB) and after rinsing it will allow finer particles to pass through, but that will correct itself after a few days.
If it a new tank, you should leave the sponge alone for a couple months and just lightly rinse the sponge to remove surface flock.
Also VERY IMPORTANT!!! I just noticed you mentioned rinsing the stone in de-chlorinated water, I hope you are not rinsing the sponge in just tap water, it could be killing off the BB colonies or at least reducing their numbers where you have a mini bloom/cycle each time you clean it.
You should always rinse it in tank water that you remove for PWC