Help, she's dying! Possible Cal or Phosphorus deficiency??

[TDZNBEER]

Hey guys,

This is my first grow, so learning a lot here.

I've felt like I've been battling a cal and mag deficiency this entire grow. Make small changes and I feel like she's doing well then days later it's back to the same problem. But this morning whatever this problem is has EXPLODED overnight!

Problem: Plant is 40 days old, 1.5 weeks into flower. Very yellowish, spotting and curling leaves. It starts at the bottom and is now moving to all top growth. Roots are looking great, from what I can tell there are no signs of root rot.

Current setup:
13 gallon DWC
General Hydroponics flora series - Last night I increased her feed thinking this was a cal/mag issue. Gave her 5ml per gallon CALiMAGic, 5ml pg of FloraMicro, FloraGro & FloraBloom then topped off with 2ml pg hydroguard (All in that order). Total ppm of mix came out to 890, PH at 5.8 and holding.
Horticulture Lighting Group HLG 300 V2 Version 2, 3000K (sitting 20in away from canopy).
Running 24 hr light.
RO water (I'm on community well and our water is terrible. 700+ ppm coming out of the tap!).
Strain is Mexican Airlines autoflower
3x3 tent
Temps average 75f-81f
RH ranges 40-45%, it was 60% in veg.
Res temps average 62f-65f
4 air stones in res.
Res changes every week, sometimes sooner.

 

[Simplicio]

If you are using the 500 ppm scale, your ppm is much too high.
I think it's too high even if you are using the 700 scale.
You are also giving them too much light.
Lights are too close, and 24 hours of light will cause stress.

If I had those plants, here's what I'd do right now:
1. reduce feed to EC=0.8 (ppm500=400, ppm700=560) or less. Allow CalMag to be about 1/4 of this ppm.
2. Raise lights to 36 inches.
3. Use 18-6 lights.

I personally have tried 24-0, 20-4, and 18-6.
The way I grow 18-6 works noticeably best.
Growing with more than EC=0.9 causes nute burn for me.

Less is more with these plants.

Here's the best fertilizer strategy I've found:
If ppm falls from day to day, the plants are eating fertilizer and leaving water behind, so increase ppm.
If ppm rises from day to day, the plants are drinking water, and leaving fertilizer behind, so decrease ppm.
Wrong feeding also causes pH to go haywire.

 

[TDZNBEER]

Hey Simplicio,

Thanks for your reply!

I am using the 500 scale.

I'm still learning how to measure feed to get to my desired PPM. Using the PPM range you've given me, how much of each product per gallon should I use?

Since the plant has been on a 24 hour schedule, would reducing now cause it any stress? Should I gradually reduce it over a period of time?

I did notice with this new feed, the PPM has risen 10 points since last night. But she's drinking almost a gallon of water a day. PH is still sitting at 5.8.

 

[Simplicio]

Hey Simplicio,

Thanks for your reply!

I am using the 500 scale.

I'm still learning how to measure feed to get to my desired PPM. Using the PPM range you've given me, how much of each product per gallon should I use?

Since the plant has been on a 24 hour schedule, would reducing now cause it any stress? Should I gradually reduce it over a period of time?

I did notice with this new feed, the PPM has risen 10 points since last night. But she's drinking almost a gallon of water a day. PH is still sitting at 5.8.

I measure ppm with a meter, and have no idea about volumes.
Make a test gallon using known amounts, then you'll know for sure.
My test gallon told me 1 g Greenleaf megacrop produces a ppm of 125, and my calmag gave 140 ppm.
Changing light an hour or 2 per day is fine.

 

[MMMi]

900 for dwc is very high. Not sure I ever got much over 500. You may be locking out calcium, not deficient.

 

[TDZNBEER]

Would I need to do a complete res change to bring down the PPM or could I pump out a few gallons of solution and replace with PH'd RO water to dilute to the desired ppm?

 

[MMMi]

You can dilute, but in general if you are trying to fix a problem -- best start with a fresh solution. Or dilute a couple, replace a couple and see if either helps.

 

[TDZNBEER]

You're right, it would be best to start fresh.

So best practice would be to measure ppm while I'm adding nutes? In the past I've been measuring by volume based on nutrient schedules.

Thanks again for the advice guys! I'll post an update in a few days.

 

[MMMi]

I think most nutrient schedules are quite high. DWC needs lower nutrients in general I've found.

I only do ppm myself, but I use dry nutes.

 

[Simplicio]

DWC absolutely needs less nutes than other methods.
I never go above 450 ppm, and am at 220 ppm right now nearing harvest.
My experience is that plants ask for the most food during the stretch, and then keep asking for less and less until harvest.

You can change ppm anyway you want.

As an example, if my 15 gal reservoir is at 450 ppm, but I want it to be 400, then an approximate calculation is
450/400*15 = 16.9 gal is what total volume would be needed to have 400 ppm.
Crudely, the 2 gal difference could be used by adding 2 gal plain water, or by removing 2 gal, and replacing them with plain water.