[CO2 drop checker solution won’t go in]

I’ve gotten an FZONE CO2 drop checker from Amazon. No amount of tilting and turning it seems to get the solution to go into it. It won’t go down past the turn. Does this sound like the device is bad or am I putting the solution in wrong?

[Otocinclus deaths]

They really like to eat Repashy super green. You can make a batch and keep it in the fridge ready to go for a couple weeks.