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Do they look any different than the regular ones?
We will find out soon enough :p

Root mealies are bigger and fatter and greyish, not much like the little green or black ones

Ohh nasty!
I was just repoting some small ones and there was some white/grey stuff around the roots. A bit like very fine spiderweb... or mold. Could that be them?

Did you see anything that looks like a big, fat grey aphid?

Nop..
But there were mealybugs on the plant itself too. So I thought that could be it.