Yellowing problem, detailed, with pics.

Indoor drip system

15 Gallon reservoir with 4 of the 14-16" air stones. 2 water pumps, 1 that pushes water to the drip head and 1 that keeps the water circulating in the rez.

Watering 3 times a day for an hour each time. 6:00am-7:00am, 2:00pm-3:00pm and 10:00pm-11:00pm. 1/2 gph heads

Lighting is 18/6
2 4' florescent fixtures both with one cool and one warm bulb and two random 18" "plant lights" I had from previous mycology experimentation. (Very successful.)

2x2x2" rock wool cubes embedded in hydroton clay pellets

4 weeks old from seed.

Water is from tap, PH 8.1. Lowered with ph down to 6.2 and left to sit for 24 hours to remove chlorine. PPM 175-185 after the 24 hour period.

Humboldt Grow/Bloom/Micro. Pictured at end.

Nutes are mixed in a one gallon jug and then stirred into the rez with circulation pump on. Solution is at PPM 500

I've had a problem with brown algae but that seems to have cleared up with adding a pump to create circulation and 2 more air stones. That is to say I've cleaned my rez thoroughly and then reestablished it with no further signs of algae.

However I've been getting these yellow spots on my plants, not all have shown it yet. It begins in the lower leaves, old growth. It shows up from the leaves stem side at the base and spreads over the leaf uniformly to the tip.

I've looked over the "Have A Plant Problem? Check Here First." thread and have narrowed down my problem some.

There is no browning or upturning of leaf edges. So I've ruled out Nute burn, Phosphorus, Potassium, Magnesium, and Iron problems.

I'm thinking maybe ph flux as I've had a problem keeping it stable. Over the last few days things have leveled off to 6.5 and I'm currently slowly trying to lower it. It has never been outside the 5.2-6.8 spectrum before. I do have a PH meter and calibration solutions. However my issue only seems to be growing worse.

I was looking at over watering but I'm only running 1 1/2 gallons over each plant a day with 7 hour dry periods in between. Also in the photo it seems the affected area is in leaf tips, my yellowing starts at the lower vein section of the leaf and spreads outwards. There is also no wilting in my plants as you can see in the photos.

Nitrogen is a maybe, but, the plants growth is quite exceptional.

Zinc is also very probable as the photo shown in the "Have A Plant Problem" thread looks very similar to my issue, only much further advanced in it's progress.

Sulfur is also probable due to the yellowing in the photo, however the plants leaves seem to be growing very quickly and without trouble, if they are not of normal size, I fear to see normal.

With so many things it could be I've decided to ask you guys, as many of you have far more experience than I. I've tried to be specific, if you have any questions please ask.

I've included photos to help with the diagnosis.

Thank you for reading my txt wall and any help.

Thanks for the detailed writeup. It may just be a combination of over watering and high pH.

pH: Your setup is hydroponic so you are looking at a pH of between 5.5 and 6.0 across the period of your grow and budding.

Watering: probably cut it back to half an hour instead of an hour. Watering 3 times a day is fine, you could up that to more, but I think its the length of time the roots are being watered in combo with the slightly high pH, that may be causing an iron deficiency which results in the leaves losing their green like that.

Quick fix is to change the watering cycle, drop the pH to 5.5-6.0 and perhaps get some additive that has micronutrients in it in particular calcium, magnesium and iron, and foliar spray them for a few days.

Thanks for your reply Jonus.

I'll be shortening the duration of watering and increasing the frequency.

Should I continue to slowly lower the PH or should I go all out and drop it into the 5.5-6.0 range?

Jblack277 said:

Thanks for your reply Jonus.

I'll be shortening the duration of watering and increasing the frequency.

Should I continue to slowly lower the PH or should I go all out and drop it into the 5.5-6.0 range?

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Its a bit like anything you do growing, slow is good. But from 6.2 to say 5.8, should be able to do that quite safely over a day.

what is the run off ph ? id guess it id higher than 6.5, keep an eye on it imo.

Well you could get your hands dirty and use miracle gro like me heeeeee sorrry Im a newb too with hydro but Ill be watching for the solution. The main problem is your pics. They are too blurry. But as for yellowing of leaves can be a sign of about 10 things. Most common would be overwatering. That is from what Ive read so far but Im still learning.