New to DTW - runoff measuring with rockwool grow cubes, flushing

Major Blazer

Major Blazer

Well-Known Member
Hey guys, as the title of the thread says, I'm running a DTW style configuration for the first time so I'm looking for some tips from those experienced with DTW, especially with rockwool as a medium. I'm not running into any issues whatsoever but I've been measuring my runoff and my pH is always coming out a little higher than what goes in - about 5.7 being fed, 6.4 as waste. As I understand it, this is more than likely due to underfeeding so last night I refreshed the res with a hotter nutrient solution. Measuring the runoff I was down to 6.1 pH after that feeding. Am I on the right tracks here in getting this style of grow dialed in?

Also most of what I read regarding DTW is with coco and flushing seems to be a incorporated throughout the grow. Do you rockwool growers do the same? And how do you gauge when it is an appropriate time to flush?
 
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boostedhonda

Well-Known Member
Never grown in rock wool but I run a dtw system with coco, if I have an issue I check runoff ppm. Otherwise I just adjust ph going in and adjust my feeds accordingly to their life cycle. I never flush...plants get fed up to five times a day with a lil runoff. No need to flush even at the end of flower
 
rkymtnman

rkymtnman

Well-Known Member
i do dtw waterfarms. never checked runoff since i started. i just feed really lightly once a day until runoff. i just flipped them and i'm only at 2-2-1 micro/gro/bloom mL per gallon of well water.

i would imagine with RW that you don't want it to dry out ever?
 
curious2garden

curious2garden

Well-Known Mod
Staff member
Major Blazer said:
Hey guys, as the title of the thread says, I'm running a DTW style configuration for the first time so I'm looking for some tips from those experienced with DTW, especially with rockwool as a medium. I'm not running into any issues whatsoever but I've been measuring my runoff and my pH is always coming out a little higher than what goes in - about 5.7 being fed, 6.4 as waste. As I understand it, this is more than likely due to underfeeding so last night I refreshed the res with a hotter nutrient solution. Measuring the runoff I was down to 6.1 pH after that feeding. Am I on the right tracks here in getting this style of grow dialed in?

Also most of what I read regarding DTW is with coco and flushing seems to be a incorporated throughout the grow. Do you rockwool growers do the same? And how do you gauge when it is an appropriate time to flush?
Click to expand...
@Grandpapy do you flush for retained salts in Rockwool?
 
Major Blazer

Major Blazer

Well-Known Member
I've been taking measurements of EC now too and I think I've been on the right track. I also have been reading deeper and it doesn't seem like I should ever have to flush. I still haven't found any directly touching on it though but since its never even mentioned, it may be safe to assume it's not needed.

@rkymtnman I have been keeping the medium in a saturated state to some degree, feeding once daily - I wonder if even this is excessive.

All I can say is that the plants are looking fantastic so I can't be too far off track but I'd still love to hear from anyone who has direct experience.
3wks 2 days into flower
IMG_5523.JPG
 
rkymtnman

rkymtnman

Well-Known Member
Major Blazer said:
I have been keeping the medium in a saturated state to some degree, feeding once daily - I wonder if even this is excessive.
Click to expand...
i don't know much about RW but it would seem that if it dried out totally, it would have to retain some of the nutrient salts.
 
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boostedhonda

Well-Known Member
Just like coco, RW maintains adequate levels of oxygen in the medium. Wet/dry cycle is more for soil grows, there is still somewhat of a wet dry with dtw but not as drastic. For me in coco it’s more of a soaking wet/ wet cycle. Dtw in any soilless medium is hydro and should be treated accordingly. Each time you water you are not just giving them more nutes, you are replenishing the nutes removing excess salt buildups and MOST IMPARTANTLY! Bringing fresh oxygen into ur medium. Lower you nutrient strength and up your number of feedings per day and I bet your yield will increase.
 
Grandpapy

Grandpapy

Well-Known Member
curious2garden said:
@Grandpapy do you flush for retained salts in Rockwool?
Click to expand...
When I was running cubes I was feeding 2-3 times a day, letting the tray fill up covering all, but once the pumps shut off I'd pull the drain plugs so it drains fast, pulling fresh air into the cube as the feed drains.
I had great results using H&G but the salt build up was insane, (dont tell the g/f i tried to clean the cloth bags in the washer) It's been 3 years since I've used h&g but still have a few bags that wont give up their acquired salts. (and I'm too cheap to toss em)
My issue with rockwool was I would get about 20% of them with a different density that wouldn't drain as fast as the others even when using a friction reducer. (sm-90)
 
curious2garden

curious2garden

Well-Known Mod
Staff member
Grandpapy said:
When I was running cubes I was feeding 2-3 times a day, letting the tray fill up covering all, but once the pumps shut off I'd pull the drain plugs so it drains fast, pulling fresh air into the cube as the feed drains.
I had great results using H&G but the salt build up was insane, (dont tell the g/f i tried to clean the cloth bags in the washer) It's been 3 years since I've used h&g but still have a few bags that wont give up their acquired salts. (and I'm too cheap to toss em)
My issue with rockwool was I would get about 20% of them with a different density that wouldn't drain as fast as the others even when using a friction reducer. (sm-90)
Click to expand...
Thank you
 
T

Treej96

New Member
boostedhonda said:
Just like coco, RW maintains adequate levels of oxygen in the medium. Wet/dry cycle is more for soil grows, there is still somewhat of a wet dry with dtw but not as drastic. For me in coco it’s more of a soaking wet/ wet cycle. Dtw in any soilless medium is hydro and should be treated accordingly. Each time you water you are not just giving them more nutes, you are replenishing the nutes removing excess salt buildups and MOST IMPARTANTLY! Bringing fresh oxygen into ur medium. Lower you nutrient strength and up your number of feedings per day and I bet your yield will increase.
Click to expand...
I loved that!! I was having issues with RW PH run off being to high(5.6 going in)(6.8-7.0)run off!..I would nute @(240TDS) and it would come out at like (80-120TDS)run off..what do you think?
 
Star Dog

Star Dog

Well-Known Member
Treej96 said:
I loved that!! I was having issues with RW PH run off being to high(5.6 going in)(6.8-7.0)run off!..I would nute @(240TDS) and it would come out at like (80-120TDS)run off..what do you think?
Click to expand...
I dkk about your run off situation but getting lower out isn't unheard of.

Provided you put ph 6.0ish in ignore what comes out it's irelevant if the plants healthy.
 
P

ProcessSpecialist

Member
Treej96 said:
I loved that!! I was having issues with RW PH run off being to high(5.6 going in)(6.8-7.0)run off!..I would nute @(240TDS) and it would come out at like (80-120TDS)run off..what do you think?
Click to expand...
Your total dissolved solids (TDS) should be lower in run-off. Measuring TDS is measuring the organics present in your feed (i.e nutrients). It would be a greater concern if your supply and waste/return was measuring the same, you would be dealing with zero nutrient intake. Same goes for waste pH...the chemistry of the water is altered after passing through the medium and root ball. This is the entire reason DTW is argued by some to exceed recirculating...you don’t have to constantly adjust a pH variables from return runoff (waste) - you simply supply an optimum feed and send the less than optimal Waste-to-Drain!
 
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