Post more information! Are you using ent_create + ent_clone (a lot)? ent_clone has many limitations (such as increasing memory), check them in the manual and the forum.
AFAIK you cannot decrease the nexus size manually.

"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual

Check out my new game: Pogostuck: Rage With Your Friends