Diagnosis Needed PH?

[MountainWalker]

Hello all, I am going crazy trying to figure out what my issues are with this yellowing that happens right around day 32 every time in my plants, and then around week 7 the fan leaves end up all brown and dead, seemingly having the nutrients sucked completely out of them. Any help greatly appreciated.

1. Tahoe OG clones
2. Just started week 5 flowering, vegged 1 month.
3. Plant height: about 3.5 ft
4. Container size: 3g
5. Roots Original Soil, amended with 30% perlite.
6. Watering about every 3 days with RO.
7. Watered with plain RO water till about week 4, then started adding a little Karma or cal-mag (2ml/g) intermittently to the RO water so it is about 150-250ppm and then ph it to 6.3 in order to stabilize ph in the soil.
8. I just fed for the first time at week 4 with 2ml/g gro big, 2ml/g Botanicare Pure Blend Pro Bloom Soil, 3ml/g Karma , ph'd to 6.3
9.No foliar feeding.
10. Growing under 2 600w HPS in a 4 x 8 tent.
11. Plants about <18 inches from bulb.

13. Temperature about 82 F 55% rh in day, about 60-65 F rh 50% at night
14. Runoff measured at 5.4 ph
15. I know I don't have root aphids (preventative measures), maybe just a couple wayward fungus gnats, but not bad at all.
16. This is my sixth grow, and I seem to get the yellowing really bad every time around week 5 getting proggresively worse by harvest.

CO2: 1500 ppm
I am puzzled why the ph is measuring 5.4, when I've only fed the plants once during the entire 8 weeks they've been growing (hence I don't think it is salt buildup). The yellowing is just starting to get bad, but if it goes like my last grows, almost all the fan leaves will be dead and brown by week 7. This situation has me extremely stressed out, I try to be very attentive to every little detail to no avail...Thanks in advance for any tips or advice. More info can be provided as needed.
How swould I go about getting the soil ph up to a more favorable 6.0, I thought watering at 6.3 every time would have ensured this? Thanks so much for looking.

 

[legal_med_grow]

I am new to growing, but I thought this was normal due to nitrogen not being needed during the flowering stage. just curious, what did the buds look like, how much oz did you get off each plant and light, and how did the females smoke from your previous harvest? If you got decent weight and great smoke, I wouldnt be to worried. And I know someone that had a ph problem too, they put lime in there soil to keep it where it should be. I could be totally wrong about all this, just trying to help get this started for you

 

[Seamaiden]

It appears to be an issue with potassium first and foremost, and a subsequent issue with phosphorous. I personally don't think you need Cal-Mag, and I have always had issues using it and have ended up separating out the components. I think either adding dolomite lime to the mix prior to planting, or topdressing it, would be better here.

I also don't like using run-off parameters to measure anything because using that method has never helped me solve a problem. I perform a media test, which involves simply making a slurry using clean water (0ppm if you've got it) of known parameters, add the media to make a slurry, let it set for 7-10mins, then test EC and pH. I don't test EC if I've been using organic nutrients, it's completely unreliable and inaccurate, IME. Do the media test and see what you get in terms of pH. If the soil pH does turn out to be that low, then again, adding back lime will help drive it back up into the 6's.

So, the tell(s) for your issues, to me, have to do with where the yellowing and necrosis occurs, and those reddened petioles are a classic tell of P issues. And P and K must be balanced, along with Ca, in order to play well. Perhaps you might want to consider using tap water, since it has a higher mineral content, and that way the pH will be kept driven just a bit higher where it should be.

I'm also with l_m_g as far as when yellowing should occur. For an 8-9 week strain I want to see yellowing *by* that 7th week. I want that fade, you see. However, the yellowing I want to see is decidedly different from the yellowing I'm seeing on your girl there.

 

[HydroRocks]

IMO it looks like nutrient deficiency to me.

For starters you should be using a "water feed water water feed" schedule or something close to that.

By feeding with only RO water every time, your actually stripping or leaching out minerals and much needed nutrition from the soil by doing this.

Also, if your using organics, it takes time for the biology in the soil to break down the organics into something that the plants can use for food.

Another point is you cant really wait until all your food sources are depleted before adding new organic foods to the soil as it will be to late.

I would suggest you to either change your feed schedules and start using mineral based nutrients so the plants have proper nutrition available to them all the time instead of it being dependent on the vigor of your soil biology.

Stop watering with only RO water.

Cheers!

 

[MountainWalker]

Thanks guys that helps, I wouldn't be worried about the yellowing so much had my yields been so crummy, (like 1/2g per watt) although the quality is very good each time, and that's what I care about most. And SM, you the best! Thanks so much for your time guys.

 

[Seamaiden]

Don't worry too much about chasing a number as far as those yields go. You'll get there, it just takes practice.

 

[freegrow]

like madien said K lock out from CAL/MAG IMO stop cal/ mag and feed 2 times it should repair

 

[MountainWalker]

So I measured my ph the way SM suggested and get a ph of 6.2 from my soil. Would you guys say feeding them pure RO until week 4 or 5 would lead to a pretty svere defficiency, considering I've been running CO2 the whole time? I'm thinking the ladies were just really really hungry.

Also would it be possible the plants got so defficient of P and K that they could never properly recover. Thanks farmers you some good people here helping out.

 

[Seamaiden]

Yes, I would say that nothing but pure RO water could definitely lead to deficiency. I believe P and K are fairly mobile nutrients, but I did spend a good bit of time trying to right an imbalance last summer with my grow and I never quite got it right.

That pH you got, while low, is at least within range, but whatever you give them should fall within a wider range, remember that for soil it should be 6.2-6.8. Remember also that not all nutrients are available for uptake at any/all pH points, which is why you must let it range, and why that can lead to what appear to be deficiencies. Make sense?

 

[MountainWalker]

Make sense?

Absolutely, thanks again!

 

[oscar169]

If your using pure RO you have to put something back in, I have Ro water coming out of the unit at 2 PPM, then I add back to the Ro water Cal/Mag + at the rate of 5-7 ML per gallon, must times I run it up to 200ppm then water them or add the nuts to water ect :pimp:

 

[tattoojim]

If your using pure RO you have to put something back in, I have Ro water coming out of the unit at 2 PPM, then I add back to the Ro water Cal/Mag + at the rate of 5-7 ML per gallon, must times I run it up to 200ppm then water them or add the nuts to water ect :pimp:

im running my r/o with cal/mag at that same rate and see n the same issues. but not all my girls are showing the same issue?

 

[tattoojim]

cal/mag drops my r/o water ph to 5.5 from 7.0..