Leaves droppy

One litre every 2 days is barely enough to keep them alive. For plants that size, give them 3-5 litres and do not water until the top inch or so has dried out again. You need to water enough so that there is run off each time. This helps prevent nutrient salts from building up to toxic levels and is also the only way to ensure that water has penetrated all the way to the bottom of the pots, which is where most of the roots will be or be headed. This lack of deep watering is probably the reason for them looking droopy and tired. 18/6 really is best, there is little to be gained by growing at 20/4, except over worked plants. Hope this helps, Organoman.