I don’t do res changes…haven’t done it in 18+ years.
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what nutrient line do you use
I read the reasoning behind it is bio availability
when the plant sucks up the nutrient water it causes some of the molecules to react and become not usable to the plant anymore.
so instead of a root system fully submerged in usable nutrient solution, you get a less than optimal growth.
IDK if its BS or not, I am not a chemist.
in the dwc grow I’m doing now I changed the res once after 4 weeks,
water uptake slowed down and the leaf started looking burned, pH way off.
Depends on the plant too, the bubblegum in my tent needs pH up every few days because the res drops as it uptakes water.
Gary from PA Hydroponics has about the best RDWC build video that I have seen. He has a page on YouTube. You can feel free to tweak it to your personal needs if necessary. I had never tried DWC before and was fortunate enough to find these videos and tweeked the setup to fit in my room. I’m using 4 10 gal Rubbermaid brute garbage cans and a 20 gal for my reservoir. To drain I just drop a 1/4 hp pump in one of the cans with a garden hose screwed on, plug it in and pump it into my toilet or outside if I’m not lazy and give my palms, etc a little love. To fill if back up I put a 5 gal bucket in the tub, reverse what I did to drain it, drop the pump in there, turn on the water and the pump. It doesn’t pump it out too fast to the point where the spigot can’t keep up. Side note, if you built a system like this, try to throw Gary a bone and buy something from his store. Tubing, a pump, etc… Bezos has enough money. Support small business.
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I don’t do res changes or flush
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I run DWC with individual buckets, I’ve had ten going at once. No full res changes for me either unless things get really funky. I watch my ph and EC levels somewhat but I generalize, ie first two buckets are low ph everybody is going up. I also switch the plants into a different bucket every week or so to try and combat nutrient lockout. Really lazy and unscientific and it works well for me.
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I don’t check my ph or ec levels either…I use Chicago water straight from the tap and my pot turns out perfectly fine…
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I don’t do rez changes either. I just refill the bucket when it gets kinda low (which is every couple days), add nutes when the ppm gets low enough to do so. I do monitor the pH but sometimes it feels pointless. I have had problems with acid rain effect tho. It happened when I had one large pump devoted to one bucket with a large air stone. I opened a couple free valves on the air pump so as to reduce the air flow in the one bucket, pH normalized.
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I just fill the rez also unless I see the pH drop too much that it causes an issue with the plants or the ppm is drifting upwards. Done full grows with only one rez change when I flip to 12/12 
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On my 4th grow with no rez change
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You start a new grow with the water from the last one?
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Yes. When I remove the roots from the last plants I usually have to add around 20 gallons of water
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Ditto, I’m new to hydro and have been keeping reef aquariums and farming acropora coral for decades with few water changes. I felt confident enough I could balance nutrients and PH without and changes.
So far so good as I should have some plants ready for harvest in the next few weeks. Hopefully I don’t pay the price, if I missed out on some growth, good, I had to super crop two plants, and relocate another to its own 4x2x7’ tent to not have them butting against the ceiling using 6 gallon buckets 
I also haven’t used any microbes, recharge, or anything beyond the 17 needed nutrients. Hopefully I don’t get burned…
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Do you run anything through it it filter it in any way? I was thinking of running potassium permanganate and GAC through the system after a grow rather than draining and filling. But I’ll save that for my third grow.
What levels are your nutes at at the end of a grow?
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No I dont filter
My levels at the end are the same as the beginning since I adjust the levels once a week
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I’m at 1200 right now and a couple weeks into flower with autos started at 500, ramped to 800 then 1200 mid veg. Should I just maintain this level through flower rather than ramp down?
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I use Jack’s 321 so my ppm is maintained at 1200 ppm
Yesterday when I checked my rez it was close to 1400 and the level was low so I just added water.
Pretty much my story, a little spike and then top off. I’m using flora trio but will be ordering jacks RO formula since I have an RODI unit and RO unit not sure which it used… My runoff is 85tds, was thinking of using that for watering…
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I buy my RO water at a place in town. $1 for 5 gallons
I recently finished a grow and checked all my totes and everything was clean so I’ll do another run.
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It’s such a pain lugging water around. I’ve got two unused units sitting around that I was going to sell that I got from buying aquarium setups. See if you can find a cheap used one near bye, you’ll wish you’d bought it sooner
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