edges of leaves are light yellow, some plants only

I started 24 plants in small starter cubes under fluorescent lamp array (8 lamps) without problems. At two weeks transplanted into hydroton flood and drain system under 2 600 W lamps. I'm using Advanced Nutrients "Light Feeding" program. pH levels have run a little high, but never above 7; usually around 6.25 pH. All water has been run through reverse osmosis filtering system, and I change water once a week. Plants are growing well and at 4 weeks are about 1 foot high with dense, not stretched out, growing patterns. The only problem I have is that on 5-6 plants the outer edges of leaves are yellow--probably only the last 16th of an inch. At first I thought I was burning the plants at recommended 3 foot height above plant tops and raised it to 4 feet. This seemed to help--new leaves came in fully green. But now some leaves, both new and older, show the same symptoms.

If you fill-out the troubleshooting form (cut-n-paste) and provide a picture or two...we'll be better able to help.

Info using form:

24 Plants are growing in hydro solution. Indoors. Soiless (Hydroton)
System is Flood and Drain (30 gallon reservoir),
soiless, but fertilizers are liquid Advanced Nutrients "Vegetative Growth" formula. When water returns to reservoir it has varied in pH from a low of 5.75 to a high of 6.65. Currently at 5.75. Plants are now in their 4th week.
Water sourced from LA municipal water district, run through Reverse Osmosis filters (and changed once weekly). Source water pH varies slightly from an average of 6.5 (i. .e, before introducing fertilizers, pH correction Down, etc.) ppM is currently 441. The first week in the flood and drain system I kept it down to around 250 ppM.
Air temperature night and day is exactly 76º.
Lighting sources are 2 600 W Lumateks w/ Hortilux 600 W HPS
Lighting is about 3.5 feet above tips of plants
Reservoir temperature is 74º
I don't have a way of measuring humidity, but it is neither high nor particularly dry--the room is air-conditioned with 2.5 ton unit; without the plants the room would probably be a little dry, like most air-conditioned spaces; the plants and the regular flood and drain of water keep it above that, but not to the point of feeling humid.
Lamps are on 19 hours/day
Room is air-conditioned
Effectively I did presoak the media because I did "dry runs" of the flood and drain for 3 weeks while the seeds germinated and were in early growth under 8 lamp fluorescent light array. I also washed the hydroton thoroughly before putting it in buckets, although this initial wash was not with Reverse Osmosis conditioned water. But I filled and drained the reservoir twice with Reverse Osmosis conditioned water before the plants were introduced, so it's not likely that much of the salts from LA water district would have remained.

I don't have access to a digital camera, but I can describe the condition pretty well. On a typical plant some leaves (varying from a few to around half) will have a band of yellow on the outer perimeter of the leaves--widest (around 1/8th inch) at each of the points of the leaf and then tapering to around 1/16th inch on the remainder of the leaf edge. The plants are otherwise seemingly healthy: they are now about 14" tall, with dense growth. They are all females and some plants have more of this problem than others, although they're all in the same grow room with common reservoir.

Two things that I thought might be responsible:

1) The leaves didn't show this problem while they were under the fluorescents. So I at first assumed that they were shocked by the transition to HFS spectrum, and so I raised the lamps from 3 feet to 4 feet. This seemed to help, although now that they're around 3.5 feet they are still exhibiting this on new leaves, although probably a little less than on the early leaves that had the problem under HFS. If this is the problem it puzzles me because some growers recommend keeping the lights about 2 feet above the tips and even at the beginning of the growth under HFS they were at 3 feet.

2) The other possibility is that I'm drying out the leaf edges. I've kept an 18" fan in the grow room, moving it around so that every day each plant spends a few hours in what probably amounts to a 10 mile/hour breeze.

Anyone have any idea what's causing this problem?

im not a hydro guy to start but i do know a little and i would start getting a more consistant ph thats alot of fluxuation the highest you want it to go is about 6.2 i believe. so not only is it high but fluxuation confuses and stresses plants

lets see if a hydro guy rings in but there is a start

i keep my 1000w 10 in from canopy at all times from clone transplant through flower

Thanks for your post. Since reading it I've been controlling the pH much more than earlier--I'm now keeping it between 5.75 and 6.0. And I'm not noticing any yellowing at the edges of the leaves that have developed recently. So I think you've solved my problem. Shit is really growing fast now--2 or 3 new leaf clusters every few hours!

high bro, as you can't post pics you might want to scroll through this link as
Stitch really knows her stuff.

The Complete guide to Sick Plants,pH, and Pest troubles! - International Cannagraphic Magazine Forums

btw, this thread is so good it was reorganized and compiled into a book that
is available on Amazon.com for $12.00 and worth every penny!

Thanks, Bozo, for the helpful direction to MyNameStitch's Guide to Sick Plants. My plants are currently doing very well--beginning their sixth week from seed soak and the larger plants are about 18" high with at least an 18" diameter canopy; also very dense w/ multiple stems every 1" to 1 1/4".

It may be that in another week they'll be ready to go to flowering. We'll see.

As we know, we're all Bozos on this bus...:)

drp

Quote:

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Originally Posted by drpdrp

Thanks, Bozo, for the helpful direction to MyNameStitch's Guide to Sick Plants. My plants are currently doing very well--beginning their sixth week from seed soak and the larger plants are about 18" high with at least an 18" diameter canopy; also very dense w/ multiple stems every 1" to 1 1/4".

It may be that in another week they'll be ready to go to flowering. We'll see.

As we know, we're all Bozos on this bus...:)

drp

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you're more than welcome and all the credit goes to Stitch, she is the one with
the expertise, all i did was point you in the right direction as she has helped me too!
i finally broke down and bought her book so i wouldn't have to keep scrolling
through the questions and such as the book only contains pertinent data.

also, i'm really glad your plants recovered although i must tell you that i've
started rooted cuttings at 6inchs and had them finish near 24 so if that
happens for you you'll be lookin' at 6foot plants!

even if they don't, tripling in size is very common so even that will give you
54inch plants.

That is an excellent and informative link, taught me a thing or two! Thanks:)