Having some trouble with yellowing and brown spots

Reaching out for help please! This is my second try growing cannabis. The first time didn’t go so well and now I’m seeing similar issues.

What strain, ILGM Kush Mix, one each Hindu, Master, Bubba Kush

Method: Soil - Ocean Forest
Vessels: 3 gallon plastic pot
PH of Water, aged tap water is 7.5 and that's what they got the first 4 weeks, since then I've been adjusting Ph to 6.5.
Light system- Spiderfarmer 2000 at 15 inches above leaf tops
Temps; Day 75, Night 68
Humidity; Day 45, Night 65
Ventilation system; Yes, 4 inch straight pipe with charcoal filter
Humidifier yes, without humidifier it gets down into the mid 30's
Co2; no
Nutrients; Foxfarm- Grow Big, Great White- Premium Mycorrhizae

Seeds started great. Seedlings were short and stout and dark green. First 5-6 weeks of veg everything looked amazing. Then I started seeing yellowing and then brown spots. I took the Master Kush plant and removed leaves from the bottom areas and gave extra GrowBig, (I had been giving half recommended dose). Not seeing improvement, actually got worse. Got a Ph meter and corrected 7.5 tap water to 6.5 after letting it sit for 3 days. Now at week 8 and not seeing the dark green I want. Plus more yellowing and brown spots. Plants are growing with 8 or 9 tops each that should flower but new growth is light green and 2 nodes down things look bad. Have seen female pistils on each plant so they seem rowdy but I don’t want to cut lights to flower when leaves look like this plus there’s still plenty of room to grow in the tent and I haven’t introduced a scrog net yet.
So I hoped correcting the water Ph would correct a nutrient lockout if that’s what it was but I haven’t seen improvement so now I’m thinking it must be something else. Over watering? I’m giving them just enough to see some flow out of the bottom and about 3 days apart. Before I water I heft the pot and they feel light after 3 days. Grow Big has a lot of nutrients in it so I thought I had that covered but maybe not. Some of the bigger older fan leaves lower down seem a darker green like when they first sprouted 3 weeks ago so perhaps that’s a clue. I’d say it seems like yellowing is more pronounced at the top of the plant. The yellowing starts between the veins of the leaves. That might be Manganese deficiency, Potassium excess? I’m not sure. The brown spots look the most like Manganese deficiency on the online picture charts but Grow big should be supplying that. Does anyone see the answer?

These yellowing issues seem very similar to my first grow so that has me thinking what has changed and what is the same. I have new, different seeds. New, different soil. New, different nutrients. I have the same tent, same light, same pots, still using tap water aged uncovered at least 3 days but now I’m adjusting Ph to 6.5. I’m not sure which way to turn yet.

Do a runoff test for both TDS and PH. If you don’t have a TDS meter, they’re cheap. I suspect nute burn. FF should carry you out to 8 weeks without supplements.

FF also recommends a flush at intervals.

When you get the meter you can set a specific TDS when you add nutes as well as doing runoff test.

Thank you Myfriendis410 for your suggestions. I have given them a good flush and I am investigating a TDS meter. I have used a Ph meter many times in my previous work experience but I’ve never used a TDS meter. Can you tell me how one reads the results of this device in regards to the practical monitoring of nutrients?

TDS meter reads electrical conductivity like a PH meter and converts into different outputs: PPM 500, PPM 700, EC. If your nutrient line calls for 900 ppm (500 scale) then you mix and dilute as needed and simply measure the solution directly. TDS meters are cheap: $15 will get a good one.

I would say u need some cal/mag and u need nitrogen ur plants are hungry i would say ur soil has hardly any nutrients left in it

Is the light cranked up full power. At 15 inches seems pretty close and might be a slight bit of yellowing from the lights. The spotting would be something totally different but the top parts of the plant looking alot more yellow seems like the light is a bit much at this point. I’d raise the light up 2 or 3 inches and give a good calmag feed and see what the runoff numbers are.

I’m a bit confused that Myfriendis410 says “I suspect nute burn.” and Tezza2 says " i would say ur soil has hardly any nutrients left in it". Are we looking at the same pictures? These 2 comments seem at odds.

Also, although I’m new at cannabis cultivation I do have a science background and so I’m thinking wouldn’t it make more sense Mark0427 that if I suspected a Cal/Mag deficiency and if I had the TDS meter, that I would test first and then add the nutrients if I found that they were needed? What would I do if I added nutrients first and then when I tested I found they were off the scale? I’d have to flush them right? My general rule should be KISS right? Perhaps there is some aspect of Cal/Mag that I don’t understand?

Anyway, I gave them a good flush as Myfriendis410 first suggested and although I have not seen much change in color they are growing out new leaves prolifically and when I had them out of their saucers I could see some nice thick white roots coming out of the bottom.

If I offended anyone in my comments above I assure you I mean no disrespect. Social media can be quite a challenging form of communication and I’m someone who started out with a rotary phone.


Calmag will not harm the plant adding it to water only days. Now if u had an over abundance of it in the plant would pose an issue but having ff nutes they contain no calmag so it is suppliments into the mix and from sounds of it u have not added any to the regimen if it is something I believe would harm the plant I would tag a more knowledgeable fella here but to add calmag will do no harm mostly good. If calmag was not in the soil to start I’m guessing u would be in a worse predicament than u r. Myfriends is a super intelligent guy and I would follow thru with what he says as he has multiple grows compared to most. I don’t see it as being nute burn either as u say I just gave nutes if I read right. I’m leaning towards slight sun burn or a calmag issue as there hasn’t been any added yet calmag is required on water days especially when u use distilled or ro water as it does not contain any trace minerals or very very minimal of them. My ro comes out at 2 to 4 ppm so no calmag and just water makes my plants wonky also

No offense taken here. Everyone is able to do what they want with their plants. But that’s just my guess up there on the issue. When u flushed it u flush out all the nutes and all so basically down to just a soil and roots so u need to get the nutes back up again. I’m still thinking add calmag to this mix and u’ll fly high

Thank you for your comments. I was interested in your previous comment Mark0427 about the height of the light and it took me a while to find the website where I got the information I was working with but here it is.

So with a review and testing data the author recommends 15.5 inches and notes that the light doesn’t really cover a 2’ x 4’ tent out to the edges. Mine has been in the 15 to 17 inch range in a 2 x 4. The seedlings looked amazing to me because they didn’t get tall and spindly like my first grow when I hung the light at 24". This time at 15" they were short and squat with huge dark green leaves so I thought that was an improvement. They sure looked healthy to me at that height. There wasn’t any sign of yellow till about week 5 or 6 and that was after I started giving GrowBig at 1 tablespoon a gallon on 3 occasions in weeks 4 and 5, 2 cups per plant. So that didn’t seem like very much nutrients to me. I was just giving them a nudge. I’m working as Myfriendis410 suggested I shouldn’t have added any. Well I’m gonna watch them for a bit and see what happens.

OK, so a few days have gone by since I flushed the plants and they look a little better. The new leaves growing at the top have a little better color. I’ve gotten some Cal-Mag and a TDS meter so I’ll be giving them some of those nutes soon and start monitoring the TDS. Here is a picture of the Bubba Kush at 4 weeks when it seemed like a greek god of health ans vitality-

and this morning, which is 5 weeks later when it looks sickly, with small, yellow leaves, some twisted, some with brown spots. I think by now it should have been a foot taller then it is and ready to flower.

Here are some pics of the stem and leaves at the top.

Well I’ll see what happens. The next time it’s ready to water I’ll give it some Cal-Mag and see if that helps.