yeah, you change the water every week, although i hear it's fine for 2 weeks.
the changing is due to a couple of things really. one one side, there's the stagnation. old water is bad water. secodnly if you replace the water, you are giving it an exacting amount of feed again. After 2 weeks you might check your EC (basically a number, low means needs more food, high means lots of food in laymans terms) and figured you needed to double it's strength so add X amount of ABC, the stuff in the tank, reading off as say 1.8 could be nothing more than the leftovers that the plant didn't really need, so it would just be counter productive to add more of it. fresh water fresh start.
i will have a total of 3 totes. all identical, meaning i can just swap lids around etc. 2 totes are in the flowering and 1 in the veg. the veg tote will get it's clones, rot them out and then have the rest of it's 4 week veg time growing. at 4 weeks it'll go into flowering, and i will also take 4 more clones that day. 4 weeks later the first batch will be halfway through and the second batch wil go in. 4 more clones. when they get to 4 weeks, first batch is harvested, and 3rd clones go in. and repeat. and repeat.
obviously my 4 week schedule will go absolutely to shit but huzah, simplicity maybe! i've yet to see the power of hydro so the clones are only about 10cm tall, i don't want to be overcome by trees and not have light for them all. not to mention larger and more plants would mean the water would be drank faster meaning you might need to replace water more often.
when you empty it, the roots also get an air bath, which apparently they apreciate.
my clones have only had about a week of growing so there's a very small amount of vegging (i say vegging it's half veg half bloom cus i'm spaz) nutes, and they're now in a new tote of water with half strength bloom, which will be increased to ful strength in a week, maybe sooner. these will then go like this until near the end where i'll try some boosters etc and then plain water for last week. hydro is supposed to be a faster turnaround so i'll have to keep my eyes open for when to change what, but i'm never really on the ball anyways so haha.
should mention. i also have 2 totes, which are filled with water the day before each change to evaporate the chlorine, but ideally i'd like to route a tap or hose into my bedroom or something, as they ent sublte and i don't trust that much weight sat ontop of my tent (the tent sits on a floor that is at a 35 degree angle, and is propped up by two thing pieces of wood

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