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

[JohnC]

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.

[DW2]

Howdy JohnC. The fact that the plant is not taking up the water indicates, to me, that the growing temperatures are too low. Plants rely somewhat on the temperature difference between the water and the air. The water temperature should be between 65° F and 72° F and the air temperature should be 80° to 85° F. At lower temperatures the plants slow down their uptake of the nutrients.
Also, what is Your water source? I have noticed that some folks on the site seem to have pH problems when using RO or distilled water. I use the tap water (and it is hard water, a blend of well and lake waters). I mix the nutrient and the fill water to a pH of 6.0. At the mid week top off I check the pH (usually around 6.75 to 7.5 pH) and add water adjusted to 6.0 pH to top it off. I quit trying to balance it in the reservoir between feedings because I killed a couple of plants during one grow by over correcting the pH. I now let it vary as it will and I have a lot less stress on my plants and myself!
Good luck with Your grow.

[JohnC]

Thanks for your response, @DW2.

I grow in my basement so don't have much options in the way of raising ambient temps. I can say that the plant doesn't appear to be growing slowly. In fact, shes growing quite fast, almost too fast.

I am using RO water purchased at my local grocery store.

I think I'm gonna do another res change today using my RO water, but this time I'll adjust my nutrient level to around 300 ppm. I'll then wait to see what happens after 24 hours and go from there.

This is really causing me headaches and I feel helpless. I sure wish I could figure this out.

Just a thought - Maybe I don't have enough air exchange in my grow cabinet and my air pump is pushing CO2 into the reservoir, driving down PH?

[D.A.A.S.69]

Morning JohnC, I don't have any experience in DWC,but I was just wondering are your nutrients fresh ? How long have you had them?
I wish I could help, but I can't think of anything you ain't already done.I sure hope you find out though.

[Jason]

If you are not using an air stone in your rez, add one or two. 02 naturally raises pH and is antibacterial. All my pH adjustments are pH down as a result.
I check my Water Farms three times a day and usually adjust 1-2 times a day. Always pH down.

[JohnC]

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 nor 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.

@D.A.S.S.69 - My nutrients are only a few months old, having just purchased them prior to starting this DWC back in August.

Jason - I do have a dual-outlet air pump feeding two air stones as detailed in the DWC tutorial on the GWE website.,

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

[Flockshot]

In my limited experience 65F has been the magic number for me. Above 65 (at all times) I can manage to keep them growing. At 65 or below during the dark period, bad things have happened every time.

[JohnC]

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.

[tvbfe]

Everything looks great to me man, grow on

[Obi-Wan]

Are you adding pH up or down to your nutrients when mixing them? If so how much and how long do you wait before taking your pH reading? In my limited experience I have found it is best to thoroughly mix after adding pH adjustments and wait 15-30 minutes before taking a reading.

[GanjaGed]

Was this happening before you lowered the PPM?

There's several things that can account for this.

• Small reservoirs are very susceptible to PH fluctuations
• It's not uncommon for PH to raise during veg and lower in flower
• Algae - check sides/bottom of res for bio-film, check air lines etc.
• Dropping PH combined with static water and PPM levels could indicate to much oxygen causing an acid rain effect

There could be other things also but these 4 are often the culprit.

[JohnC]

Obi-Wan - When mixing my nutes up, I always add my Cal/Mag first, let that "rest" for a while (1 to 2 hours), then add my HydroGuard, again letting that rest for a bit (30 minutes or so). I then add my nutrients (GH flora micro, gro, & bloom). Finally, after letting that rest a bit (15-20 minutes), I adjust for PH. I've been adjusting to a bit above 6.0 before swapping out the reservoir water.

GanjaGed - Yes, this has been happening for some time now, several weeks. All I've been doing is adding 1.5 to 3.0 MLs of PH-Up to the reservoir daily.

Adding the heating pad several hours ago has already made a significant difference in my growing environment. The ambient air temperature in the cabinet now is 71 degrees. Reservoir water temperature has increased to 65.7 degrees. Will keep monitoring to see where temps stabilize at.

[Obi-Wan]

Ok, I use the same nutrients with the addition of Orca by Great White, we are fairly close in ppm and we use similar sized reservoirs . The only difference is that I use tap water around 150 ppm to start with while your ro water should be close to 0 ppm. When I mix my nutrients I mix everything in succession with only a good stir in between, I let it rest for 30 minutes and then check pH. It will normally require .75ml of pH down to bring me to around 6 but every once in awhile it takes more, I can’t explain it, but it does. I always start with .75ml, check pH, and then let the mix rest for another 30 minutes and then recheck the pH. 9 times out of 10 my pH is 6.2 after .75 ml of pH down and then 5.9 after 30 minutes. After 3 days it has ranged down to about 5.5 at which point I top off the reservoir with pH 6.5 water.

[JohnC]

Thanks for those details, kind sir. Once my temps stabilize, I'm hoping my little lady will rebound a bit and start eating / drinking.

[JohnC]

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. PPMs remained steady at 340 PPM.

[Jason]

Why is your PPM so low? I don't measure it, but looking at my GH feed chart for Flora Trio, my Week II solution is supposed to be 1050-1350. The lowest noted is during Ripen, Week 11 at 750-1150.
Ranging pH is a good thing as different nutrients are absorbed at different pH. Mine always ranges up due to 02 from the air stone.
You have something I've never encountered going on.
Good luck.

[JohnC]

Why is your PPM so low?

Well, with a dropping PH like I'm experiencing, the typical causes are:

-- A bacterial / algae infection at the roots (already ruled out)
-- Nutrient strength is too high (I was feeding at 900 PPM but cut it back as a troubleshooting step)
-- Somehow, I'm in a CO2-rich atmosphere and I'm pumping CO2 into the reservoir (have no way to check the CO2 concentrations)

I've exhausted everything I can think off and I don't know what else to do.

[Vapo69]

Have you tried calibrating your ph meter dude?