HELP! DWC Hydroponics water PH drops over time

[FlyingDutchPaddy]

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

[FlyingDutchPaddy]

Quick add:
Temperature is around 75F,
Humidity varies between 53% - 65% during the day.

[Steveo h]

Keep your reservoir temp between 62 and 68 degrees.

[Cloud]

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.

[Obi-Wan]

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.

[IslandColas]

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?

[D.A.A.S.69]

Hey Paddy, it's gonna drift, but your PH, needs to be between 5.5-6.5 for hydro.
6.5 is getting kinda high.

[Campesino]

I am curious. What is happening with your EC? Is it falling also?

[DW2]

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!

[Grinder]

Very sound advice.

[Sockfilter]

FlyingDutchPaddy, To answer your question as to WHY it drops, well I dont know the 100% reason, however I do believe that it has to do with Cation Exchange Capacity (CEC) and even if doing DWC, the CEC happens and appears to be the norm. Maybe Campesino can chime in on the reasoning as I am still trying to wrap my noodle around CEC as I do believe it is a much bigger issue with coco growers.

http://www.greenhousegrower.com/production/fertilization/understanding-plant-nutrition-nutrient-sources-media-cation-exchange-capacity/

[Campesino]

Yeah, he isn't totally wrong, but he seems to think that the buffer is less stable than most other sources. I link to him especially because he grows in particularly small containers and really demonstrates that container size is irrelevant to the size of the plant in Coco.

And I agree that pH is altered by certain exchanges in the media. But I believe that pH can be buffered as well. I believe that the difference in the water that you described is a result of the different capacities of the starting waters to buffer pH. For example, it takes a lot less pH down to adjust a gallon of RO water from 7.0 to 6.0 then it would to lower well water the same amount. The RO water would be stable at the new pH quickly and the Well water would take a while to stabilize. This is a result of the water's capacity to buffer the pH.

EC rises in the media because of the removal of water through evaporation and transpiration. The nutrient exchanges with the plant have minimal impact on the EC of the solution.

[Sockfilter]

Thank you Campesino, so nice that you are able to translate info to layman terms..

I was thinking exactly this as you stated in your coco grow:
"EC rises in the media because of the removal of water through evaporation and transpiration. The nutrient exchanges with the plant have minimal impact on the EC of the solution."

Agreed on the buffer of both the Well and RO. One of my theories is that yes that roots do an ion exchange that can offset it's stable state, however the nutrient solution is also exposed to the air which does a little exchanging CO2. So the nute solution is always trying to reach pH of 7.0 unless super buffered. So in theory the nute solution should remain stable if properly buffered, yet the actual EC raising is NOT due to the addition of more salts (unless no proper runoff), but due to the evaporation of water which makes it appear that there is more salts.. Like a traffic jam, all the autos are the salts and not enough road is the H2O of sorts..haha

Apologies FlyingDutchPaddy for sub-thread highjack, just helps me to write this mess out..

[Campesino]

Sockfilter Yes, that all sounds pretty good.
pH certainly changes as a result of interactions between the nutrient solution and the plant and media. In general these changes are not problematic and can be ignored. pH of inflow should be adjusted - pH of run-off should be ignored
EC doesn't change because of interactions with the plant. EC can change due to interactions with the CEC of the media - but shouldn't in properly buffered Coco. Therefore, Evaporation is responsible for the changes to EC - and EC should always be higher in Run-off than Inflow. Run-off prevents it from becoming too much higher.
Finally, if the EC of run-off is lower than inflow in Coco - this indicates that the CEC is not buffered and the Coco is still stripping Ca and Mg from the nutrient solution.

Apologies for continuing the hijack - and Cheers to all

[FlyingDutchPaddy]

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.

[DankwingDuck]

The brown roots don’t look like rot . Likely just nute stain .

[Campesino]

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.

You should really rectify this! You need to track EC in a Hydro grow!!! Meters can be had for about $15 ... http://a.co/eCEJQ83

[FlyingDutchPaddy]

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

[IslandColas]

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/forum/growing-community/get-help-for-marijuana-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?

[Campesino]

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/forum...u-need-to-know

[FlyingDutchPaddy]

@IslandColas,

I don't spreay at all for bugs. Growtent is free of all insects.
The only thing that I did see once was a long-leg spider sitting in the corner, havnt seen it recently.

[POKEDSMOT]

Don't rinse your roots with tap water. Your pH is ranging fine.

[DankwingDuck]

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 .

[IslandColas]

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

[FlyingDutchPaddy]

Right, today's update.

I came home and found pH to be 5.5 exactly.
I decided to change all the water.

as suggested earlier i let the water wait for 5 - 15 mins before measuring pH after mixing nutes, and added just enough pH down to bring it to 6.5.

Reason for pHing to 6.5 is that I keep noticing that it drops over the course of a few days (4 - 6) to below 5.5.

Tap water (from a private well) is 7.5 (waited 15 mins for it to settle).

15L water + 62ml Micro brought down to 6.4 with 2ml pH down.
15L water + 31ml Gro brought down to 6.3 with 2ml pH down.
15L water + 92ml Bloom gives 6.5.

Nute schedule is for flowering stage as per nutrient schedule for bubbleponics found on this site.

After adding all to system and allowing to rest for 15 mins, pH stable at 6.5 in all 4 buckets & resevoir.

Water recirculation pump capacity = 600L/hr

Looked for EC meter, thing here costs €90.
Got a small fan now mounted in the top of the growtent for a gentle breeze at plant level.

Will keep updates going as I measure.

Noticed one of my plats had something looking like banana's.... Could she be herming?
Pic attached.

Thanks for your time

[DankwingDuck]

you can get cheap meters on Amazon . I think I paid 15$

[FlyingDutchPaddy]

Campesino , expecting my TDS meter Tuesday...
Was around €27 including shipping.

[Campesino]

I think you'll be happy that you made the investment. It will really help you to know what is going on and allow you to fine tune your grow!

I'll be happy to help if you have any questions