I'd go with something in a 400-550 gph range. Remember? 4'-long tank
Yeah, it can get expensive, ~$40.
I'd put it 2-4" below the surface, around the same as your spray bar. You will have to play with the positioning a bit to see where the flow goes.
One of the best ways to save $$ and do good for your plants is to buy dry chemicals here on TPT and mix your own fertilizer. For <$40 you get enough to last you a year+, big savings over buying Seachem stuff which is ~90% water. I can give simple steps on how to mix them with water and my formula, if you want. Takes 30 mins to mix enough for ~3 months and 1 min 3 times a week to add it to your tank.