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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?
drpdrp Reviewed by drpdrp on . 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 Rating: 5