I don;t know anything about coca soil... but 300ml of water to a plant occupying a 10 litre pot does not sound like a lot to me...

again... not knowing coca soil, watering every other day also sounds like alot to me, but that also depends on the size of the plants, strain, ambient heat, etc. that might be perfectly normal for your situation.

from what you describe (leaves curling upwards from the sides), is not a sign of over-watering i believe... taking a look at this page: Grow Marijuana FAQ, Cannabis cultivation - marijuana growing tips & photos the symptom of those leaves could be a magnesium deficiency... but you didn;t mention yellowing of the leaves, so... that also doesn;t really fit, but i don;t know what else would cause the leaves to curl in that pattern... hopefully somebody with some more knowledge will chime in for ya

take my comments with a grain of salt though - i am pretty far from being a cannabis growing troubleshooting expert