is filter needed?

What kind of filter are you talking abut? Are you talking about an Undergravel filter? All tanks need a filter, unless you plant to never have fish in it.

~ MyShrimpDied

A heavily planted tank of healthy, actively growing plants may well NOT need a biofilter. But you do need current in any case, so it is conservative to use biomedia in the current-generating filters, just for insurance and safety.

And with that current, you need to establish a balance between fish and plants.
Years ago, when starting out, I used to visit frequently, a man who bred and raised fish in a hatchery here in Jersey.
He had, what I at the time, considered the most beautiful 50 gal. tank with nothing but Crypts. and two beautiful breeding Discus.
No filtration, but daily water changes.
He used to say, 'it's all about balance'. I'll never forget that tank.......or the man. Learned a lot from him.

Len