Can you do bubbleponics without water pump??

I recently made my first DIY 4 site bubbleponics. I dont have all of the accessories yet and was needing alil help. Do I have to buy waterpump or can I just let the mist from the bubbles do the job?? Also what size rockwool is needed? Do I use that throughout the entire process? Any help or suggestions is appreciated. heres a pic of my setup so far. I just started learning two weeks ago so dont be too harsh lol. I have 400hps and MH.....should that be good for 4 plants? Also ave 2 air pumps (60 gallon) and 3 12in stones. Im using an 18 gal res.

no u dont need the waterpump , an airpump is what must of us just use for DWC.18gallons is fine for 4 plants.as for the size of rockwool well that just depends on you and how much media u wanna put around the rockwool to stop the light from hitting the bottom.are u using hydroton"clay pebbles"?