What's causing yellowing leaves and leaf tips curling up?

Hello, I’m at week 10 of my auto feminized Northern Lights. Two plants. Growing indoors in a 4x4 grow tent. The leaves have been yellowing for several weeks and tips at the tops of the plants are curling up and browning and seem to be getting worse. I’ve checked soil ph. and meter shows ph of 7-8 but ph test strips of the water run-off show ph of 6. I did add 1 tsp of white distilled vinegar to my last watering. Not sure if I’m under fertilizing or over fertilizing, under watering or over watering? Using LED grow lights 600w. The fertilizer I’ve used since flowering started is FoxFarm Tiger Bloom 2-8-4.
Here are two photos from today of my plants. One plant is close to harvesting, tricomes are still clear. Wondering what I can do to help the other plant that has several more weeks to go. Many thanks for your help.

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Hi @EJS welcome to the forum.

It’s easier to diagnose issues with a photo taken under normal white light. Based on what I can see and your mention of 2-8-4 I’m going to guess it’s an excess of phosphorus, which may be exacerbating deficiencies in other nutrients like manganese. If you’re in a proper bagged soil, you shouldn’t have radical deficiencies to worry about, but phosphorus can lock out other nutrients.

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Thanks for getting back to me. Should I just cut back on fertilizer? Just use plain water for a while on the plant that has several weeks left. I’ll just use plain water from now on for the plant with the clear tricomes. I was using the lowest dilution of fertilizer and fertilized about every other watering. So maybe too much. Each plant is in a 5 gal fabric pot and I used Recipe 420 organic soil. Will the end product/potency be effected by this issue? The plants look so terrible with all the yellow leaves and curling tips.
Thank you.

A good ph meter and tds meter will take a lot of the guess work out. Those ph strips aren’t the best indicators.

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Thank you! Good advice. I’ll get a better ph meter. What’s a tds meter?

Total dissolved solids. It can tell you the strength of the nutrients you are putting and and what’s coming out. The measure by ppm

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Thank you! That would help with the guessing issue of too much or too little.

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How much are you feeding this plant and how frequently? Be as specific as possible please. Like ml/ltr.

I’m afraid my fertilizing was probably too aggressive.
12/06/2019 seeds first sprouted
01/02/2020 fertilized with liquid Alaska Fish Fertilizer 4-1-1, 1 tsp per quart per directions on bottle
01/07/2020 fertilized w/Neptunes Harvest Rose & Flowering formula 2-6-4 white stigmas showing on both plants. 1 Tblsp per gal. per instructions on bottle.
01/10/2020 fertilized w/ ½ strength 2-6-4 Neptune’s and ¼ strength 5-1-1 AK fish fertilizer on both plants
01/17/2020 fertilized with liquid FoxFarm Tiger Bloom 2-8-4 2 tsp to gal of water
01/20(?)/2020 liquid FoxFarm Tiger Bloom - plain water followed by diluted Foxfarm tiger bloom
01/23/2020 liquid FoxFarm Tiger Bloom - 4 tsp to 2 gal. water
01/31/202 added 1 tsp to 2 gal of water with 1 tsp of FoxFarm Tiger Bloom.

Meant to say on 1/31 I added 1 tsp of white vinegar (left that out) to 2 gal of water with the foxfarm fertilizer

So you’re giving the plants tiger bloom in the dilution Fox Farm prescribes at every watering?

every auto i have grown has brown or yellow leaves never figured it out think iy’s just the life cycle hers my grow notice the leaves this is my 7th grow and every one had brown or yellow leaves before harvest 105 035 138 054

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i use fox farms soil happy frog straight up but only use 1/2 the dose of recommend dose i also use vinegar to adjust the ph and that seems to be the most important. i would not worry the autos they will just grow weather you do anything or not . give em good p/h water and good soil . and enough light then just watch them bud done it 7 times since last year never had one die from neglect or to much anything and i did make some major errors the plants are just so resistant to most stuff because of the rudellis that make them auto flower . so bottom line they will be done before you can kill them . it only take about 70 days max most mine were more like 65 … less worry more enjoy the grow and smoke it will be fine …

Keystone Cops, to answer your question (I was cut off last night, reached the ‘13 post limit for first time users’ )
I’m using the Tiger Bloom per the instructions but have diluted it for some of the fertilizing. The bottle says 2 to 3 tsp per gallon every other watering for general watering. I’ve been doing 2 tsp per gallon, but a couple times just used 1 tsp. (looks like I’m at the limit of my posting for first time users. I guess people must get carried away when you finally find someone who can answer your questions)

Mrstock55, thank you, that is very reassuring to hear. What strain are you growing? Are those Northern Lights? Though my plants don’t look great, on one of my plants the buds look terrific and are covered with glassy tricomes. The other plant is further behind but has lots of potential flowers showing.

So you are alternating plain water and fertilized water?

Yes, for the most part. I kept track when I fertilized but didn’t record plain watering. Next time I will keep better records! I believe I used plain water every other watering. With the yellowing leaves I got caught up in trying to figure out what was wrong and my record keeping got lax (should have become more detailed! ). First time nervous grower. A bit overwhelmed. I did an outside grow a couple years ago with a friend and it required much less fine tuning than this grow tent, in the winter, in an unheated room. But I love it!
Thank you for your responses and much appreciated advice.

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I think it’s safe to assume the manufacturer’s schedule is about 2x what a new grower should run. Their plan might assume you’re under way more light than you are, and that you’re optimizing in other ways.

Anyway, I’d dial it back to 1/4-1/2 what you’ve been doing. Continue watering like normal, allowing the container to get dry before watering again. See how the new growth comes in. That’s what I would do.

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Will do! Thank you!

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