When doing a PWC, does it matter if I take the water from the top half of the tank or the bottom half? Are nitrates distributed throughout the tank evenly, or do they sink to the bottom of the tank( or is there a higher concentration of nitrates at the bottom?) I am planning a PWC soon and I dont know wether or not I can just scoop water out of the tank with a gallon jug, or if I have to go out and buy a vaccum to siphon the bottom. I am not concerned with fish waste matter, and uneaten food because the bottom stays pretty much clean.