The thing about a filter is how, after a while, a bacterial cycle gets established which gets rid of ammonia and nitrites.
It can take a month for the good bacteria to set up shop.
If you change your filter, you reset this process.

I think tadpoles can live in remarkably filthy water. I'd say don't buy more equipment until you know you have an issue.

It's not a very long term thing. I vote for keeping the filter you have and upgrading only if it obviously fails at its task.

I wrap my intake filter with bulk media. That saves all of the tiny babies, especially the cherry shrimp.