Possible Magnesium defficiency but want to be sure. +rep to all that help

Hey Im growing some Island sweet skunk and one of them seems to have a deficiency. See the link in my signature for all the info on my setup. It looks like a magnesium def. but im not sure. below are some pics, I noticed it yesterday morning which is when the first pic was taken. all the rest were just taken. let me know what your thoughts are. any help is appreciated
Thanks
JP
-first day
Top Leaf not as bad as the bottom

What are you growing them in and feeding them?

jphebbie2 said:

See the link in my signature for all the info on my setup.

Click to expand...

make it easy on those that want to help you and put your setup here so we dont have to go and find it, just makes helping you that much easier.

for sure, Im using FFOF soil. I put them in the fairly large, I think 3 gallon, containers they are currently in just after they rooted, which in retrospect wasnt a good idea because they wont dry out. I havent watered them in 6 days and its still fairly damp a few inches into the soil. They are about 2 weeks into veg being as I potted them in soil 21/2 weeks ago. I have only given them one 1/2 strength dose of FF grow big about 12 days ago. other than that only good rocky mountain tap water that is about 6.8PH. they are vegging under a 400w MH bulb right now. I have plenty of air circulating, about 200 CFM in a 2x2.5x8ft space. I want to give them a bit of epsom salt water but i dont want to over water. Only 1 of my 3 plants is showing this sign. it was the fastest growing and I topped it 3 days ago. Mag def. makes the most sense but I dont want to make the problem worse by trying to fix something thats not the problem. hope this is enough to spark some feedback. There are a lot of pics/ info on this grow in the link in my signature or just shoot back with some more questions. Any help is always appreciated.
Thanks
JP

Yes it does look like Mg def. which is a little unusual considering the Worm Castings and Kelp that the Grow Big is supposedly made from. First off, you should check the soil's Ph if you haven't yet. Soil and water Ph are two different readings. Once you've checked that and adjusted if necessary, give her a full strength dose of the Grow Big at the next watering. Always alternate feedings with plain water. There are no signs of nutrient burn so go ahead and up the ferts until the tips of the very bottom leaves start to brown and then pull back the nutes a bit.

probably have too much calcium and its causing mag def

lower your ph to 6.3-6.5

So I just watered with half dose grow big and half teaspoon epsom salt. will that be a large enough jolt of Mg to turn things around a bit? Ph of runoff water was about 6.3ish(its hard to judge from the color), and soil reading was low at 5.5 but my meter is a piece so I think thats innaccurate. It jumps all over the place and never gives the same reading. Ill get a new one in a few days when i get a pay check. for now we will see what the nutes will do. hopefully it wont get worse. Ive read it will take upwards of a week to for this to turn around. Does that sound accurate? Thanks for your help everyone. Much appreciated as always.
JP

Runoff Ph is a pretty inaccurate measurement. I'd go with your soil tester. You can purchase little capsule-type soil test kits for five or six bucks and they will tell you how accurate your probe is. You can then buy extra capsules when you run out and want to verify your probe's results.

Yes, changing soil Ph does take awhile. Transplanting is the only way to really change soil Ph quickly. Throw some lime on top and watch the soil Ph, sticking the probe as far down as you can. Adjust the water and fertilizer mixes you use to something like 7.2 so when it mixes with the acidic soil, the average Ph is closer to normal. Adjust liquids closer to normal as the soil Ph is corrected.

Call a few garden centers and ask what their most long-lasting Ph meter is. I've made the mistake of buying the most expensive digital meter in the hopes that it would last the longest. It turns out an analog one half the price lasted twice as long, and still going.