Last grow I alternated between top and bottom feedings, once the plants were fully vegged and into flower. I use soil in 5 gal smart pots. When I top water, I stop when there is a decent amount of runoff in the large saucers. I vacuum it right up. When I bottom water, I pour about 1/2 Gallon of water into the saucers and watch the plants suck it up. I go back and add another 1/2 gallon to each saucer after a few minutes. My theory is the bottom watering is good for dry tops (less gnat risk). But, I need to run water through all the soil via top watering as well (to flush salt).