Huge image

Guys, I've a bloated image and I don't know why it's so huge and how to shrink it.
It happened that my image has grown from 50MB to 440MB in a morning.

I've already followed these suggestions https://github.com/pharo-project/pharo-core/wiki/Memory-Hogs and flushing monticello repos the image reduced itself to 219MB, better.

Anyway I don't know how to reduce it more. Evaluating: SmalltalkImage current reportCPUandRAM I found

Class                                          code space # instances  inst space     percent   inst average size
ByteString                                           2625       58054     196795872       85.50             3389.88
Bitmap                                               3748         357       9586748        4.20            26853.64
Array                                                3084      151758       6889008        3.00               45.39

....
Total                                             8758122      786830     23026087299.60000000000001

you can see ByteStrings occupy 85.5% of space!

I tried to inspect instances of ByteString, but I can't find anything worth of. If I Open pointers to the instance I find references to GLMPanePort, GLMPane and NodeModel (see attached png)

I'm on Pharo 4

TIA
Davide