DWC PH issues: Ph dropping like a rock - Please help

[John1961]

Good morning folks,

I am having some PH issues with my DWC and I really need someone with experience / knowledge to help me understand what the hell is going on.

My DWC consists of a 10-gallon tub filled with 5 gallons of water. This DWC is supporting a single plant that has been growing strong for 12 weeks now. I just flipped the lights to flower yesterday.

It seems that on a DAILY basis, my PH drops at least 1 to 1.5 full points and I'm having to add 1.5 to 3.0 MLs of PH-Up to the reservoir to get my PH back into an acceptable range. My water level does not drop that fast and my PPMs are staying stable.

For example, not 20 hours ago, I took the following readings from my plant environment:

- Air Temp: 64
- Water Temp: 62.7
- Humidity: 32%
- Water PH: 6.0
- Water PPM: 590

This morning, I took the same readings:

- Air Temp: 63
- Water Temp: 62.5
- Humidity: 30%
- Water PH: 4.8
- Water PPM: 590

I had to add 3.0 MLs of PH-Up to get my reservoir PH back up to 6.1. My water level did not drop overnight and my PPMs remained the same at 590. I've been using 10ml of Hydroguard with every reservoir change and my roots look fine & bright. The water smells fine and there does not appear to be any signs of root rot.

I've attached my feeding schedule and as I just flipped to flower yesterday, I changed my reservoir and followed the "Week 6 - Transition" nutrient levels at 1/3 strength.

Can someone please help me understand why my PH is dropping like this on a daily basis?

PLEASE HELP.

 

[rkymtnman]

My water level did not drop overnight and my PPMs remained the same at 590.

that's not good especially water level.

i would add plain water to cut your ppm's in half and see if they start eating and drinking.

62 is a bit chilly too for water temps. can you get it up to 65f?

 

[John1961]

Thanks for your response, @rkymtnman .

With my PPMs already at 590, wont I starve my plant if I cut the PPMs to around 300?

 

[rkymtnman]

Thanks for your response, @rkymtnman .

With my PPMs already at 590, wont I starve my plant if I cut the PPMs to around 300?

well, they arent eating or drinking now which is a problem.

do it for a day or two. say you cut it in half to 300, and the next day it's at 250,that's good, so add some more nutes and shoot for 450 to 500 ppm.

make sense?

 

[John1961]

Yes, it does @rkymtnman. Thanks.

I'll do another res change today, setting my PPMs around 300 and wait to see how she responds.

 

[John1961]

Good morning, folks. I'm back with an update though I don't know if I'm any closer to a solution.

Yesterday, I did a reservoir change, cutting the nutrients by about half from the previous change. After several hours of bubbling away, I captured the following readings:

- Air Temp: 65
- Water Temp: 62.7
- Humidity: 32%
- Water PH: 6.1
- Water PPM: 350
- Water EC: .7

This morning, after the lights have been on for an hour or so, I captured today's readings:

- Air Temp: 64
- Water Temp: 62.6
- Humidity: 30%
- Water PH: 5.5
- Water PPM: 350
- Water EC: .7

As noted, my PPMs did not change overnight. Also, the water level went down only slightly, maybe a 1/2 quart. That suggests to me that the plant is not drinking that much. Since the PPMs / EC didn't change, I guess that means that the plant is neither taking in nutrients now do I have nutrients leaching out of the roots into the reservoir. Yet my PH dropped significantly overnight from 6.1 to 5.5.

I just don't know what to think with the PH dropping like this on a daily basis. I live near a rather busy road so maybe I have elevated levels of CO2 in the air that are in-turn getting pumped into the reservoir where the molecules bond readily with my RO water. If that is the case, then I guess I have no choice but to drop 1.5 to 3.0 MLs of PH-Up into the reservoir each day in order to maintain PH in the proper range.

I think I'm am going to do another reservoir change today. I want to get my EC readings back up to around 1.2 (I am at .7 now). Since I just flipped to flower a day ago, I expect the stretch to commence and she'll be hungry.

Any thoughts? I really feel like I'm floundering here and need some guidance.

 

[rkymtnman]

I think I'm am going to do another reservoir change today. I want to get my EC readings back up to around 1.2 (I am at .7 now). Since I just flipped to flower a day ago, I expect the stretch to commence and she'll be hungry.

i would keep it at .7 for another day or 2. if they aren't eating at .7, they definitely won't be eating at 1.2 even if they do start eating, there is no way it will drop .7 overnite. so you'll have time to bump it up when required.

you sure you don't have any root rot going on?

the only other thing i can think of is that they are kinda stalled right now as you transitioned from veg to bloom. what light cycle did you go from and to? 18/6 to 12/12??

 

[rkymtnman]

one thing i just noticed in your pic is the airpump is in the closet. can you get it outside the closet so it's drawing in fresh air??

and i have a plant in veg right now that is just about the same size and it drinks a 1/2 gal a day. so 1/2 a quart is not good

 

[smokebros]

As @rkymtnman mentioned, a significant pH drop overnight while PPM's remain the same (or go up), indicates the nutrient levels in the res should be lowered.

One thing that should help is to leach the salts out for 1/2 a light cycle. Do this by emptying the res and filling it with plain PH water, but add the water into the res by pouring over the hydroton/medium/net pot.

When you fill your res back up with nutrients do what @rkymtnman suggested and aim for 300 PPM's.

Thanks for your response, @rkymtnman .

With my PPMs already at 590, wont I starve my plant if I cut the PPMs to around 300?

No.

 

[firsttimeARE]

I only get pH drops late in flower if I feed too much. How big are your plants? 1.2EC isnt a lot. I mean it is the max I feed my plants. But so long as they arent tiny they shouldnt be causing issues.

 

[John1961]

Here are a few pics from today. She's been growing for about 12 weeks now; I've trained her using the main-lining method and I have eight tops ready to flower. I flipped the lights to 12/12 just two days ago. She is about 22 inches in height above the lid of the reservoir.

I've included a pic of the root mass as well as a top-down look from above the plant. To me, the roots look OK, there is no smell or sliminess.

The top-down pic, showing that yellowing, suggest to me that the plant is hungry.

This morning, I added the black rubber mat you see leaning against the right side of the cabinet. It is actually a "foot-warmer" pad that does a good job of radiating heat. It has two settings, low or high, and works really well to add some heat to the cabinet without going crazy with heaters, heat lamps, or anything along those lines (I used it last winter in the same cabinet with a soil grow). Since adding it to the cabinet about an hour ago, the ambient air temp has risen to 68 degrees and my reservoir temp has risen to 63.5 degrees. I am going to continue checking the air and water temp hourly to see how much the temps go up and what they might stabilize at.

 

[rkymtnman]

I've included a pic of the root mass as well as a top-down look from above the plant. To me, the roots look OK, there is no smell or sliminess.

agreed

The top-down pic, showing that yellowing, suggest to me that the plant is hungry.

i think they are nute locked. i didn't notice your temps. you need to get it up to 75F in the cabinet. get water temps to 65F to 68F.

when i've had nute lockout, i've flushed for 24 hrs with RO water and then start back on light nutes. sounds counter-intuitive to starve them when they are hungry but they aren't eating now so you've got to do something to get them back eating and drinking

 

[drgreentm]

I agree with rkymtnman, at your temps plants uptake of nutrients is more than likely slowed to a crawl. Temps with light on should be in the low to mid 70s. Yes plant looks hungry and ones first reaction to this sign is to feed more but if the plants unable to utilize the food given it's for nothing. Correct temps, flush for 24hrs and start back on 1/4 to 1/2 strength nutes and all should be well.

 

[John1961]

Good morning, folks.

Well, the heating pad has helped a lot by stabilizing my temps. Air temps in the cabinet are at 68 to 69 degrees. Reservoir temps are steady at 66.8 degrees.

However, as expected, my PH dropped again overnight. 20 hours ago, my PH was 6.1. This morning, it was 5.3. So I added 2ML of PH-Up to the reservoir. Water level dropped a bit less than a quart overnight. PPMs remained steady at 340 PPM.

 

[John1961]

Anyone have any suggestions? I'm ready to trash this whole DWC and go back to soil.

 

[firsttimeARE]

What nutrients are you using?

This is weird and not typical behavior in veg at that feed level.

How big of a container is that plant in?

 

[John1961]

@firsttimeARE - I am using General Hydroponics Flora trio (Flora-Micro, Flora-Gro, and Flora-Bloom). The tub is a 10-gallon size and I keep it filled with 5 gallons of water.

OK, so I went to my supermarket today to buy some fresh water. What a surprise this has turned out to be. The "RO" water I have been buying tested to a PPM of 220 and a PH or 6.9. These are not the values I would expect from RO water, which should have a PPM of 0.

So now what do I do? If the supermarket water is not what it is claimed to be, do I just use tap water (PPM = 180, PH = 8.5) and stop wasting money on store-bought water?

This doesn't explain why my PH is dropping so much each night, but I do have to wonder about this water I'm using.

 

[firsttimeARE]

Use tap water and find out. Your water is most likely fine.

I only use tap and I dont have issues.

Those nutes are fine. What ratios are you using of each?

 

[John1961]

@firsttimeARE - I was feeding at about 1/3 strength based on GH recommendations. Since I just transitioned into flowering, I used the following amounts when I changed out my reservoir this past Sunday:

Total Water Volume: 5 gallons

• GH FloraMicro: 20ml
• GH FloraGro: 15ml
• GH FloraMicro: 20ml
• Technaflora MagiCal (Cal/Mag/Iron supplement): 20ml
• HydroGuard: 10ml

With the above proportions, my water would test at about 550 ppm. I generally only needed to add 1ml of PH-Up to get my water to 6.1 PH or so.

 

[firsttimeARE]

Ditch store bought water and continue with what youve been feeding. 550ppm minus 220ppm starting water is only 330ppm. Thats not enough for a plant that size.

Just play your pH changes.

I used to get 5.5 to 6.1pH rises daily. Not much different than 6.1 to 5.5 drops.