Kratky is indeed a Deep Water Culture hydroponic method. Generally when folks talk about Deep Water Culture they mean more complex builds with filtration and aeration systems. These are 'active' hydroponic systems. Kratky setups are a passive hydroponic system. Also called non-circulating hydroponic systems, they don't require pumps, filters or air stones. The simple system exploits the way plants exhale water taken from the roots into the air. As the water level drops it provides oxygen to the root zone that only increases as the entire plant gets larger.