not sure how much water to give plants

i have 6 plants on day 27 of 400 watt mh. theyre all over a foot tall some 18 inches tall. theyre in 3 gallon containers and im not sure how much water to give them. im giving them 500 ml of water every other day but thier getting so big im not sure if thats enough.

They look healthy to me bro. Just keep up with what your doing

yeah, if anything, you're watering too much, but they look good.