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HELP! DWC Hydroponics water PH drops over time

F

FlyingDutchPaddy

New member
Hi everyone! i'm new to the forums and i'm on my first grow from bagseed.

My setup:
Lighthouse growtent 1.2m x 1.2m x 2m
PLANTiT DWC Aeros IV -> 4 20L buckets + central 20L resevoir
Budmaster G.O.D 4 LED light
RAM air blower with carbon filter attached.
(No fan for air movement, though I need to get one.)

What i've noticed now that my 3 plants have started flowering is a few days after a complete reservoir change that the pH of the water drops fairly quickly.
Using the GHE trio of nutrients; FloraMicro, FloraGro and FloraBloom.
For 45-47L of water I add 62ml Micro, 31ml Gro and 91ml Bloom.

When I do a complete water change, I'm adjusting the pH after adding nutrients down to 6.5.
Before putting my plants back in their buckets, I wash the pebbles clean with 15L of clean tapwater per plant.
All done, pH in the reservoirs is around 6.5.

I check the pH every day and I'm noticing that it drops by about 0.2 - 0.3 every day.
4 to 6 days after the change the pH around the roots will be 5.5 ish, and can drop even further to 5.1 by day 7-8.

Observations:
Roots of all 3 plants are colored brownish, but not slimy at all.
Roots seem to be tangled together,
Have seen new white root growth.
Plants themselves look happy enough, though some older leaves develop small brown spots on them.
Temperature is around 75F,
Humidity varies between 53% - 65% during the day.

My biggest question is: why does the pH drop so fast after a water change?

Will post pictures of roots & plants on next water change.

Thanks :)
 
Im having the same issue. Im using 18gal totes and filling it up with 10gal. Im using the same nutes as well. Didn't start doing it till 4 weeks into flowering phase.
 
I use the flora trio and pH drift is can happen, it’s not an issue as long you adjust it when it goes out of range. In my setup I see the most drift in the first 2 weeks and it generally settles in when the plant has a solid base of roots in the reservoir. I have a couple questions....How are you circulating the water between the buckets and the reservoir? How many air stones do you have and how large is your pump? How long do you let your nutrient solution sit before adding it to your plants? Are you adjusting the pH of the fresh nutrient solution? I try to let my nutrient solution settle for at least 30 minutes before I check the pH, it gives a more accurate measurement.
 
As long as you’re staying on top of it you’ll be okay. Don’t let it drift more than a full point or you can be seriously hurting her. I’m guessing it’s mostly to do with nutrients. If you’re variables are all correct and your light-proof with the res. Plus sterile, plus holding a proper water temp (Which is CRUCIAL in DWC) then the only thing that can cause the ph to fluctuate would be your nutrients. Also what grow media are you using for the net pot?
 
Howdy FlyingDutchPaddy, As the plants use up the nutrients in the water, the pH will change, this is normal. I let the pH vary (different nutrients are absorbed better at different levels) and only adjust it when I feed and when I top off the reservoirs at mid week. During the first couple of grows I 'chased' the pH all over and nearly killed my plants. I guess that the rapid change of the pH level in the reservoir can shock the plants. Now I just adjust the pH at the feeding and add pH'ed water at mid week. The plants seem to like it and it is certainly less stress on Me!
 
I am not sure that it has to do with CEC. In fact, I am not sure there is a CEC in hydro. Cation Exchange Capacity is the media's ability to hold and exchange cations, In Hydro, water is the media.
Often, pH will climb and EC will drop in a reservoir. This is a sure sign of bacterial infection in the Res. This is why I was curious about the EC. I am not sure what would cause the pH to consistently drop. I am leaning towards Obi-Wan 's thinking that it may be something like sampling error (drawing samples or adjusting pH before pH settles).
 
Hi everyone,

thanks for your thoughts so far.
When I came home I measured pH again stright from the buckets (air bubbling & all) - got 5.7.
Water was completely changed this sunday (5 days ago).

To answer the questions posed so far, I'll list them:
How are you circulating the water between the buckets and the reservoir?
- There is a smallish water pump in the central resevoir that leads to a 4-tube splitter that feeds all 4 growing buckets. (will need to check the capacity)

How many air stones do you have and how large is your pump?
- 4 air stones, one in each growing bucket.
- Pump capacity currently unknown.

How long do you let your nutrient solution sit before adding it to your plants?
- I clean out all the buckets first. once clean, I put the buckets back in the growtent while the plants are outside sunbathing with roots in a container with some water in it.
- between placing the buckets back in the tent to putting the plants back in, i need to fill up a container 3 times with ~15L of water each time.
- while filling the container, I add the nutrients, one variety each container.
- when the container is full, I pH the water to 6.5 & then fill the reservoir with the 4 buckets attached by interconnecting hoses. I do this 3 times.
- once the buckets & resevoir are full, i check pH one more time, and its usually 6.5 when finished.
- then i place the plants back.

Are you adjusting the pH of the fresh nutrient solution?
- yes.

Also what grow media are you using for the net pot?
- hydroponic pebbles.

What is happening with your EC? Is it falling also?
- I do knot know the EC of the water, unfortunately i dont have an EC meter.

Now pictures attached of grow room and mystery plant with brownish roots.
Not sure if its suffering from root rot.
 

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Interesting, I could have sworn that I read that somewhere, ! can see the CEC between the H2O and coco, so what happens between H2O and roots? I just figured there would be at least a Cation Exchange (no need for capacity) working while the roots uptake only what it needs and leaves the rest in the solution and thus directly affecting the makeup of that solution.

Although not a standard practice anymore, when one takes a run-off pH reading it can be way out of whack as compared to the input pH, yes not fertigating enough will cause salts to build up if not flushed properly effecting the EC reading, So if the EC is way out of whack, then I would assume that the pH is out of whack (yes irrelevant to coco w/ proper fertigation). In DWC we have no run-off and it just stews in rez until it is changed or solution is acted upon by addition of more nutes, pH adjusters or getting the funk in the rez/roots.

Coming from flood/drain tables to coco, I definitely recall my rez pH's shifting slightly over the days which I found very beneficial in regards to the different nutrients up-taking at various pH sweet spots,

Will dig down the rabbit hole further..haha
 
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Yes in hydro plants just take what they need from the water. In other mediums like coco or soil there are colloids in the media that will exchange cations with the nutrient solution. In Coco, colloids will release K and grab Ca. That is the most significant aspect of CEC in coco. In soil all sorts of cations are held and exchanged in different colloids.
 
Campesino , got some time Friday to look for one, fortunately I know 2 growshops around where I live.

will read up on water EC on the site & get back when I’ve got measurements.

would that also be a reason why the older leaves are getting spotty?

thanks
 
So my reply will be backed by some proven facts and then my own personal experience. I’m using basically the exact same setup for my mother Cookie Monster plant. First thank you for answering my question about the type of media! Sometimes depending on the media and if it was properly prepared it can affect ph stability and creat an unstable reservoir. With clay pebbles you’re safe from that. The only real preparation for them is a pre-rinse to remove dust and particles from bag. You good there.

Next, your roots! Don’t be afraid of that browning. I just made a discussion over the same exact topic!

https://forum.growweedeasy.com/foru...-plant-problems/211358-root-rot-or-dyed-roots

I Thought possibly the browning was rot but it really is just stained from your nutrient solution. Your roots look AWESOME! They’re super healthy, and forming a proper root ball. If you can’t smell anything in the res but fresh earthy roots you’re cherry. Now EC is a huge deal in DWC it tells you everything about your reservoir you need to know. (Other than ph) when you know your ppm you can determine how strong your nutrient solution is and that can greatly assist in determining whether or not it’s a nutrient burn or deficiency. ESSENTIAL!


Now if you’re mixing to your specs on the bottle, you’re grow formula alone at full strength should create a ppm of nearly 1000 in my experience. (Assuming you have a general 200ppm tap water, filtered is way better) I add silicon and cal-mag to my girls during veg on top of my growth formula (pureblend pro). I run what would be considered a very high ppm in my reservoir, but everyone has their opinion on proper ppm in DWC for different stages. One thing that can’t be opinion though is absorption. You’re plant can’t use more than 1500 ppm water. Anything over that you risk burning your plants or if not that just wasting nutrients your plants will never absorb. I’m very curious about what nutrients you are using and how much of what. Which leads me to the next topic.

The spots on your leaves. Now I’m still relatively new and do not have extensive experience with plant burns and deficiency but from what I remember. Burn happens on the tips, especially of new growth, then spreads and worsens from there. Deficiency affects the whole plant just like your spotting in the leaves. If you’re positive those spots aren’t from an organism than they look exactly like the spots I was getting when my girl had a calcium deficiency. Calcium is the bone structure of the plant and if it’s deficient cell walls will begin to collapse and cause spotting, reddish stems, and signs of stress. When I saw my spotting I asked my trusted growers went over to the grow store and got a bottle of cal-mag and within 24 hours of administrating the nutrients the plant was showing signs of recovering and healthy growth. I’d love to know your feeding schedules so we could eliminate nutrients.

Last question, how often do you spray/treat for bugs?
 
Here is a post on EC that I put together. It was originally written for Coco, but the effects of EC on osmosis are the same in any media.

The thing most don't seem to realize is that plants take Water and nutrients in separate processes. The nutrients make the water salty, which makes it harder for the plant to take in water. If you add too many nutrients and the EC is too high then the plant cannot get water - not getting water is what causes "nute burn".

Because of evaporation, the EC (a measure of saltiness) of the nutrient solution will (should) gradually rise in a recirculating system. This is why you need to top off with lower EC water than you use when you change out the res. You need to know what the EC is in order to know how strong the "top-off" water should be.

I won't comment on what your EC targets should be. But I will say that hydro EC can be higher than the guidelines that I provide for Coco in my post. You should have an EC target, and you should manage your res to maintain that target.

Here is the link: https://forum.growweedeasy.com/foru...-ec-ppm-and-fertigation-what-you-need-to-know
 
I keep my ph at 5.8 in hydro . From my understanding you wanna be on the lower end of th range for hydro and higher end for soil. That’s besides the point though.

I used the same nutes and I never have any drift . Now I will say my system is not rdwc, it is just a dwc and maybe the recirculating aspect of it may be what is making it drop . I set my ph at around 5.8 and it stays there always .

Drift is something you shouldn’t worry about . It is easy to fix. You should be checking your ph daily anyways , and this just forces you to not stray from actively keeping up with maintenance .
 
I would agree. 6.5 is quite high for DWC. You should aim for 6.0 and fluctuate between there and 5.8. If your looking for a .5 buffer zone I’d say keep it between 5.7 and 6.2:)
 
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