Do I have to have sand?

When I setup my 20 gl tank, I added about 2" of aragonite. Was told I needed it to buffer ph. Also thought I needed 20 + lbs of rock. I've learned some things from TRT, than you. Ive removed the sand from places that I can't vacuum easily. Taken out some rocks slowly, for more room to clean. Tank is 20 gl high not a long. tank has been going for almost 2 years, so there's not much sand left after all the water changes and vacuuming.

Can I remove all the remaining aragonite sand??
Can BB be done without a skimmer??