Light should be around 12''-15'' away from plant, and you said you have a 5 gallon pot so 1.5L maybe every 3 days. This is what I do. I have a 3 gallon pot and I water 1-1.5L every 3 days. Above you said 20 liters that's way to much lol
also make sure all the bud sites are getting light, if big...