Different pH for different lights? HPS / MH to LED / CMH

Renfro said:

I am looking for input from growers that have switched from old school HPS and Metal Halide to LED and CMH.

So I have had my veg room running for sometime and it was all dialed in. I haven't changed anything EXCEPT for the lighting. When I changed lights I measured light intensity at the canopy before and tried to closely match that under the new lights.

I was using 1000 Watt SE Metal Halide and I changed it to 1000 Watt DE CMH 3500K and a COB LED 480 Watt 3500K.

After changing the lights I am getting symptoms on one strain, StawDawg. Two plants, one under LED and one under the CMH are lacking Magnesium to me. They looked healthy before the light change and are revegging from monster cropped clones. The one under the LED appears to be lacking it more. I have added 100 PPM of epsom salt to one of the Star Dawg's feed today and misted it with 100 PPM epsom salt and RO water.

I have been feeding at 6.5 pH as always. I tested the soil with two different meters and I am getting a media pH of 5.2 right after feeding at 6.5. This is consistent with my other plants as well although they have yet to show symptoms and appear healthy.

I am using a soiless mix, Berger BM6 HP. I have been using it for a while without issues at 6.5. When I potted I tested the mix at 5.8.

pH meters are calibrated and in working order.

I hope I have provided all the required information, if not please ask.

Here are some pictures of the one under the LED:
View attachment 4289799 View attachment 4289800

and a picture of the one under CMH:
View attachment 4289801

So is there a consensus that these type of lights require more Magnesium? Different pH? What have growers that have made the change in lighting learned about feed changes and media pH?

Thanks for taking time to read all this, lol.

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dandyrandy said:

I've never run cmh etc. I wish I could try them. Stealth here. 16 cobs in ~10 sq ft. I run at ~600 w at bloom. In the 5 years or so I've found 24" works for me. I used to try to run more light. Too many issues. I could run less watts and move closer but then spread becomes an issue. Since I run less lumens at the canopy I see less deficiencies. Growth seems the same. ymmv

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