Brown spots & Leaf edges curling up (pics)!

Well, it seems like this is a pretty common problem, but I couldn't find pics that looked like my particular situation.

I've got 6 different strains going but only the Sour Diesel and Headband are showing this. They have a few leaves that have these brown spots... on some it looks like spots have merged into brown patches. It's mainly on leaves toward the bottom or in the middle... not on new growth. Also, the leaves near the top are curling up on the edges. The curling is only happening toward the top and isn't on leaves in the middle or at the bottom. (So curling and spotting are happening on different leaves)

So, from what I can tell from my searching it looks like this is often caused by a variety of things. These plants were fed there first dose of nutrients a few days before noticing the symptoms. It was a moderate dose of Humboldt Nutrients as directed on the label. The plants are 5 weeks old in FFOF soil and the other plants that I fed at the same age responded fine. They are getting adequate light and ventilation. However, when I noticed symptoms ventilation was almost non-existant because I had a No Pest Strip in for 5 days as a preventative measure. I water with about pH 6.8 water and my runoff from these plants was about 5.0-5.1 lately. This seemed really low to me, but I've heard others in Fox Farms Ocean Forest have had simliar runoff readings and done OK. I also noticed that the runoff in my White Widows was similar 5.0 - 5.2 and it seems to be doing OK with no sign of these symptoms...

Please help!!! What do you think?

Different strains are going to react differently to the same conditions. Your issue looks to be from too high of a nute concentration. Give this a read, it should clear up some of your questions.

the 2nd two pics show definate signs of mg def.add some cal-mag or magical to your feeding cocktail.should do the trick.goodluck

It shouldn't be having a Mg deficiency this early on in fresh soil I wouldn't think.

So, these curled leaves are caused by Mg deficiency only? I'll check into it but they should've gotten some Mg when I hit them with the nutes... maybe it was being locked out by the low pH or something. I don't know.

The curl could be from the roots being root bound. I've had the same problem in the past and potting them up solved the curl problem for me. It does look like it could be nute burn also with the brown spots. Good Luck

yeh man i was useing ocean forest soil also and all four pictures above look exactly the same as how my leaves were looking, the soil is hot, i wouldnt even start feeding nutes in this soil for atleast 3 weeks

The curling leaves are from VPD (http://en.wikipedia.org/wiki/Vapour_Pressure_Deficit) It has to do with the humidity, heat from your light, and ambient temperatures. The leaves are losing moisture faster than the roots can supply it. The ugly parts of the leaves do look at first like MG def, but that doesn't mean thats all it could be. You can mix 1/4 tsp epsom salts for mg without hurting it whether it needs it or not. I wouldn't use cal/mag unless you need cal and mag.

hey man the spots look like phantom Mg defecincies and the leaves looking like that. look for root aphids

The leafes on 2 out of 5 plants have brown spots and curling up. Pictures aren't the greatest. Using ocean forest soil. 1,000 whatt hps bukb in a 5x5 tent. Any ideas?