Phosphorus Deficiency? Flowering?

First grow… Quite a few weeks into flowering with my girls and I’m starting to see signs of possible phosphorus deficiency. Second opinions?

I know right now my lighting isn’t adequate and my plants stretched a good bit but I’m tying them off now so they don’t get hurt by the light… New light and bigger tent is on the way but I’ve gotta finish these two. Only the Green Crack is showing these symptoms (red stems, brown spots). The Sweet Tooth has maybe one leaf with a few spots up the vein but nothing more.

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What strain? Green Crack & Sweet Tooth
Method: Hydroponics DWC
PH of Water: 5.9
PPM/TDS or EC: After mixed each week is 800ppm
Indoor or Outdoor: Indoor, 3x3x6
Light system: 1200w LED (actual 250W)
Temps; Day, Night? 74;70
Humidity; Day, Night? 44; 55
Ventilation system: Yes Cloudline T6
AC, Humidifier, De-humidifier: NA
Co2; Yes, No: NA


I change my red every week and my nutes that go in are as follow for my 14gal:

3ml/g CaliMag, 4ml/g Flora Micro, 8ml/g Flora Bloom, 2.5ml/g Liquid KoolBloom

Had a problem with nute burn in the beginning and everything I’ve read says keep autoflower nutes half or qtr strength. Should I add more Phosphorus??

@Bogleg @Myfriendis410 hey hydro heros, help! :slight_smile:

I only have soil growing experience, but we’ll get you some help.

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Would adjusting the ph up to around 6.3 be better in flowering?

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How many weeks actually in flower @beautifulL0V3 ?


I really don’t know because they’re autos and it went so fast. I want to say maybe a month or month and a half in or actual flowering? They’ve had the pistils for a while

I thought 5.8 was optimal for hydro regardless…?

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I grow in coco which is said to be the same as hydro and give calmag every couple waterings. To much nitrogen in flower is bad. I have a white widow auto that I feed 8ml micro 12ml bloom and 4ml ginormous (about 3 weeks into bloom) with the dark green leaves and the clawing of leaves, almost looks like nitrogen toxin


During the bloom period we should use a pH range from 6 to 6.2 for a more efficient nutrient uptake. During the last weeks of this stage, we can raise the pH value to 6.3-6.4. I read this on a hydro site.

You should be able to push your ppm to 1000-1200.It does look like the plant is starting to feed on itself.

What do your roots look like? To @hornhead comment, bacterial can cause spots that looks like nitrogen toxicity. At this point only the small amount of Micro is providing N so I don’t think it’s N toxicity.

Roots look great as far as I can tell. I can try and push to 1100 ppm tonight when I change out. Should I go to 4ml CaliMag, 6ml Micro and 10ml Bloom?

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I’d add a higher amount of M/B instead of Cl/Mg. The M&B are already formulated with Cl/Mg and you will need the extra P-K to feed the buds. 8M/16B will give you 1000ppm in DI/RO water. The ClMg will raise your nutes pH so make sure it’s @5.8 when you start.

Im with this one. Calmag up p and k slightly up n out of the picture all together at this point. Tgefes enough stored itll tell you if it needs it. Calmag also supplies n. Wnough to finish flowering

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Doubling is only going to give me 1000??

I usually do full res change out every week… putting in fresh water, then nutes, then adjust pH. And top of with pH water throughout week with no nutes.

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I don’t use Cl/mg in my dwc since the M&B are already formulated with such. My tap is ~150 and when I use 8M/16B/gl I get ~1150.

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Hm, okay. My tap is 20 so I should be right around 1000 then if doing what you recommend. I will try it tonight and see how it goes this week. Will I notice if she’s recovering?

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The plant may look healthier, but the damage already seen will not go away. The plant is in the late stages of flower and all focus is now on the buds and will continue to draw nutrients from the leaves. You want to make sure you provide adequate P-K and by increasing your M&B you will be providing more of this requirement.

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So I’m looking at your one plant and frankly I see some excess N which could be causing a lockout but frankly for the point in the cycle you are in the plant doesn’t look bad. Yes; it’s behaving differently to your setup than the other plants but we see that all the time.

I would do as @WickedAle suggested and bump the TDS up to around 1,100 to 1,200 and stay on your Lucas Formula. I’m assuming something like Hydroguard is in use too, adequate air etc.

Based on appearance you still have at least 30 days to go.

@kabongster, @Bogleg (Hey, I’ve been promoted to hydro ‘hero’ haha!) @blackthumbbetty you have a wicked good eye.


Well for being my first grow I’d say it’s been pretty healthy up until this point. I actually am not using hydroguard but it is on my list for next grow. I do have like 4 air stones in there though. My roots look pretty healthy as well I think? I upload picture of those later tonight. I’m wondering how I have excess N when I am barely using any Micro :thinking: as I do 3/4/8 but I will keep CaliMag at 3, and bump Micro to 8, Bloom to 16 tonight.

My res temp stays around 69-70. I am changing to a RDWC next grow as well because moving the plants every week, especially with as stretched as they are has been a royal PITA.

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