Um, seriously, please please please fill that crack with moss/silicone.
Several folks have lost bettas bc they tried to go through the holes in the bottom of ceromic pots, got stuck and drowned bc they couldn't get to the top.
One of my bettas went into a half inch airline tube and couldn't back out. Luckily 8 was able to save him.
They think if they can get their nose inside, it's safe.