well mine do it as well, maybe it don`t take a day to make em peak up agin (more like a half) but it is quite normal, try to notice it out doors in summer time, if you get a lot or rain, afterwords look at the plants/bushes/trees, and 1,5 L per pot is about right I guess, I just water till I get a bit of run off, in 5 gallon thats about 2L, about how often there is a few things that play a role, temperatures of course but also size of plant`s and light intensity that end up in grow rate ..
etc. a big plant under a 1000W HPS late in flowering in a 5 gallon pot might need water every day or at least every second, wile a small plant in Veg under some CLFs in the same pot only need watering every 4-5 day, also one of the reasons why its a good idea (IMO) to start em in smaller cups/pots and repot on the way ( I do 3) to avoid over watering and to build up a good root net in the middle of the pot`s
hope some of this help ..