Should I get a 20g or 29g for my mollies

[Ganondwarf2]

So I have gotten 2 balloon mollies and I've been researching on them and was wondering if I should get a bigger tank for them because I have a 3g (ik it's not the best for them but I realized afterwards). I wanted to ask which tank size would be the best if I added 2 more mollies and possibly some more fish? In the current tank I have it is almost cycled with decent hiding spots for them. They are not aggressive to one another and I WC the tank whenever I see ammonia or nitrite starting to climb. I wanted to ask this question because while they swim with each other sometimes which I noticed more so today the bigger one tries to eat the poop hanging from the other (they are both female by the way). What would be the best course of action? I am also somewhat new to the hobby.

[rlederer]

Almost always, the bigger the tank the better. Bigger tanks have more stable temperature and water chemistry and allow for more movement and hiding places. Get the biggest tank that is reasonable for your particular situation.