I am growing White Widow from ILGM. I have a recirculating dwc set up using 20gal trash cans. Two for plants, one for resevoir. Is it really necessary to change water every week or two. If so, why? Just trying to learn
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You need to change your water to give it fresh nutrients. The plant will take what it needs out of the water and leave what it doesn’t need. After a while there is an imbalance in your nutes so that has to be restored by replacing the water and nutrients
Hope that helps 
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It’s a PITA but it’s necessary. I am currently running regular DWC with 14 gallon totes. I purchased a transfer pump so I can pump water in and out really fast. Makes it easier. With as much water as you have in your two plant system you probably only need to do a complete system change every two weeks.
I have a drain incorporated into my system, so all I have to do is turn a ball valve to drain it, but then I would have to tote 50gal of water from the creek. About 100 yards uphill. That’s rough on an old man. Not to mention the expense of nutrients. But it is what it is. I want to give them the best care
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You could probably go to using 5 gallon buckets for the plants, and keep the 20 gallon res. That should cut back on nutrients quite a bit, and the plants will do fine in the 5 gallon.
How much water does the whole system hold?
As long as res temps are good and theres no algae build up… it depends on you how often you do a complete change…
I run rdwc units that hold a total of 17 gallons with a 1 inch air gap between the net Cup and water and I change out all the water every 3 weeks with no issues… so basically I only add nutrients 3 times during flowering and in between just top off with good ph’d water… 
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That sucks! No plumbing near your grow? I wonder what kind of pump you’d need to go 300 feet up hill. Hose is cheap but you’d probably need a big pump.
Let me understand this (so I can use it for my own grow).
So let’s say you just switched to 12/12 light. You set your nutrients then, top off with plain PH water as needed and add nutrients when you do the complete system change?
Seems like most of the nutrient feed schedules have weekly changes in nute levels. I guess they probably over complicate. I was thinking I would add nutes during top offs (or not) to keep PPMs in a particular range depending on the stage of the grow. In fact that is what I have been doing… am I doing it wrong?
If it’s working , then no … lol
I flip 12/12 and add 3 equal amounts of the GH 3 part nutrients and some other stuff… day 1… then add good ph’d water when res gets low… after 3 weeks I shop vac out the whole system and add nutrients at a 2/4/6 … 2-grow , 4-michro , 6-bloom mill to a gallon plus some other stuff… then top off with good pH water for 3 weeks… then empty whole system again and fill with 4-michro , 6-bloom and a bunch of other stuff to boost k till the end of flower. …
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Mind you that I just harvested almost 2 pounds under a 600 watt magnetic ballast with a 45 inch × 60 inch foot print…
Quality medicine…
I would have to know more about your set up before I could give you any good advice…
Most important is your environment… plants grow when they get what they want…lol
Well damnit @peachfuzz you have me thinking now. I am more or less following the GH trio nute schedule as posted on GrowWeedEasy. It’s more or less the same schedule that GH puts out, but at 1/2 to 2/3rds the strength.
Up until a week or two ago I had been using 3.5gal buckets so I was changing reservoirs every week. In that case it was super easy to set my nutes however I wanted. But I ran into problems (due to massive root growth, so a blessing and a curse) and had to go to bigger reservoirs. I am now in 14gal totes and am planning on doing complete changes every two weeks and topping as needed. My plan was to mix nutes into water per my feeding schedule and per PPM ranges and use that to top off my buckets. Then top off with either the nutrient rich water or plain water based on how I want to adjust PPMs. Hmmmmm.
Don’t want to high jack this thread… will tag you into mine … scroll to the top to see what I’m doing…
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Sorry. Yeah I didn’t mean to hijack the thread. I’m stoned ya know so once the thumbs get going it’s hard to make them stop. 
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@peachfuzz… you’re not hijacking anything. I appreciate your input. I’ve been wondering about the nute changes anyway
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@Bogleg… Yes I have plumbing at my grow site, but it is county water with chlorine. I tried using it on my first grow and got slime on my roots and nearly lost my plants. Switched to creek water, I add Hydrogaurd, and haven’t had any problems. I’m in week 3 of flower and haven’t done a COMPLETE water change yet. I did do about a 1/2 volume change a couple of times to get my PPMs correct
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