my dwc set was on one 20/20/20 all purpose at 1 tbl spoon per gal i use 4 in a 5 gal bucket as i did not want it to be too much, i also added cal mag through the whole grow, i changed the water every 3 days a s the ph would start to drop by then, during flower i used beastie bloomz by farm fox, as well as cal mag and bud xl by house and garden, my next dwc i use farm fox line for the whole grow start to finish, both the dwc grows i did came out real nice, lots of buds and really healthy growth,
just make sure you check your ph like every other day in the bucket itself, you want prefect ph if you can for the whole grow, my first dwc i changed the water out every week but did not check ph every other day and i didnt have problems, my 2nd i checked ph every other day and she grew real nice. hope this helps