If you could send in pic but first turn your lights off so we see the true color of the plant.
Does your plant look like this ?
I’m willing to bet it does. So your problem wasn’t ( "magnesium " ) it’s ( Nitrogen )
The write up is large but I feel you need ll in for as soon as posable Copy and paste in your files for referance
Nitrogen (N) Mobile Element and Macro Element
Benefit: Nitrogen plays a very big role in your plants; this one element is directly responsible for production of chlorophyll, photosynthesis, Amino Acids, which are the building block of Proteins. The myriad of enzymes which help the plants growth in leaves stems and the how well the vigor of your plants is.
Nitrogen is the biggest mobile element meaning it can travel anywhere on the plant.
Usually the def will start on the lower to middle part of the plant, and then will usually happen to older leaves first. Then the deficiency will work its way up the plant. Your plant can be green on top, then yellowing on the lower leaves when the deficiency is starting out. Yield will be greatly reduced without good amounts of nitrogen in your plants. Sometimes in bad cases the leaves will turn a purplish color along with the yellowing.
Unlike a magnesium deficiency, nitrogen def will start from the tips and work its way back to the leaf node. Nitrogen and Magnesium get confused. The best way to tell them apart is, nitrogen deficiency starts around the tips and works its way to the back of the leaves, where a magnesium deficiency will cover the entire outer part of the leave and make the entire leaves yellow leaving the veins to stay green. If your plants are having a slow growth rate and have yellowing of the leaves, then most likely it’s a nitrogen deficiency.
Towards the middle to end of flowering stages, the plant will show a nitrogen deficiency almost always. This process is completely normal and just let the plant naturally yellow out as it uses it’s stored nutrients. This actually helps you by getting ready for final flushing and then harvesting. At this point DO NOT not use nitrogen to fix the problem. The yellowing leaves will then eventually drop off after the plant is done with them.
Parts affected by a nitrogen deficiency are: Older foliage, going to whole plant, Petioles (rare) cases.
Now for having too much nitrogen in your growing mediums or soil. The plant will have like an overall DARK green look and have delayed maturity. Due to Nitrogen being involved in vegetative growth, to much nitrogen will result in tall plants with weak stems. New growth will be very lively and plant transpiration will be high, but not always. Nitrogen toxicity can be seen when there are very very dry conditions almost as if there was a drought, which may show a burning effect. If you give your plants ammonium based nutrients they may show NH4+ toxicity, which will show a smaller plant growth and lesions that occur on stems and roots, leaf margins that will roll downward. Also the big fan leaves will have “the claw” look. The tips will point down but the leaves will stay up as if when you bend your fingers downwards. Leaves can be twisted when growing… mainly new growths. Roots will be under developed along with the slowing of flowering. Yields will be decreased, because to much nitrogen in early stages of flowering slows down bud growth. Water uptake is slowing down from the vascular breakdown of the plants as well. Too much potassium and nitrogen will lock out calcium as well.
Problems with Nitrogen being locked out by PH troubles.
Waterlogged soil and Soil with low organic matter.
Nitrogen is a very important element in the plant, all of them are but some are more important than others. For soil the best ph to have is 6.8. Why? Because at 6.8, that’s the best number for ALL available nutrients to be absorbed into the plant without any of them being locked out. For hydro and soil less mediums best ph to have is around 5.8.
Try not to keep your plants to cold, because the cold temps will cause the nitrogen harder for the plant to be absorbed.
PH levels for Nitrogen:
Nitrogen gets locked out of soil growing at ph levels of 4.0- 5.5.
Nitrogen is absorbed best in soil at a ph level of 6.0-8.0. ( wouldn’t recommend having a ph of over 7.0 in soil) best range to have nitrogen is a ph of 6-7. Anything out of that range will contribute to a nitrogen def.
Hydro and Soil less Mediums
Nitrogen gets locked out of Hydro, Soil less mediums at the levels of 4.5-5.0.
Nitrogen has the best absorption rate at a ph of 5.5 to 8.0
(Wouldn’t recommend having a ph over 6.5 in hydro and soil less mediums.) Best range to have Nitrogen is: 5.0-7.0. Anything out of that range will contribute to a nitrogen def.
Solution to fixing a Nitrogen deficiency
Avoid excessive ammonium nitrogen, which can interfere with other nutrients. Too much N delays flowering. Plants should be allowed to become N-deficient late in flowering for best flavor.
A goof solid N-P-K ratio will fix any nitrogen deficiency. Any chemical or organic fertilizers that have Nitrogen in them will fix a nitrogen deficiency., Peters all purpose plant food 20-20-20 is good, Miracle grow All purpose plant food, Miracle grow Tomato plant food, (Only mixing at ½ strength when using chemical nutrients, or it will cause nutrient burn!) as well and blood meal! If you need to give your plants a quick solution to nitrogen and you want to use blood meal, I suggest making it into a tea for faster use, where blood meal is slow acting, but when made into a tea it works quicker! Other sources of nitrogen are dried blood, Cotton seed meal which is slow acting, Insect eating bat guano which is fast acting. Bone meal which is a gradual absorption when not made into a tea.( also excellent source of phosphorus). Fish Meal Or Fish Emulsion is a good source of nitrogen and is medium acting. Worm castings, which is gradual absorption. Seabird guano, All purpose Millennia Seabird guano, Orginal Seabird guano All Purpose, Crabshell ,which is slow absorption. Fox Farm Grow Big, which is fast acting. ( can bring down your ph as well)
Here are a list of things that help fix a Nitrogen Deficiency:
Advanced nutrients Grow (2-1-6)
Vita Grow (4-0-0),
GH Flora Grow (2-1-6)
GH Maxi grow (10-5-14)
GH floraNova grow (7-4-10),
Dyna gro Grow (7-9-5)
Dr. Hornby’s Iguana Juice Grow (3-1-3)
Advanced Nutrients Mother Earth Grow (1.5-.75-1.5)
Earthjuice Grow (2-1-1),
Pure Blend Pro (3-1.5-4)
Fish Emulsion (5-1-1)
Seabird Guano (11-13-3)
Pure Blend Grow (0.4-.01-.5)
Marine Cuisine (10-7-7)
MaxiCrop Seaweed (1-0-3)
Super Tea (5-5-1)
Mexican Bat Guano (10-2-0)
Sea Island Jamaican Bat Guano (1-10-0)
Kelp Meal (1-0-2)
Seaweed Plus Iron
Neptune’s Harvest (2-4-0.5)
Age old Grow (12-6-6)
AGE Old Kelp (.30-.25-.15)
Neptune’s Harvest (2-4-1)
METANATURALS Organic grow (3-3-3)
METANATURALS Organic nitrogen (16-0-0)
So adding anyone of these above should fix up your nitrogen deficiency! Nitrogen deficient plants usually recover in about a week, affected leaves will not recover.
Now if you added to much chemical nutrients and or organics, (which is hard to burn your plants when using organics) you need to flush the soil with plain water. You need to use 2 times as much water as the size of the pot, for example: If you have a 5 gallon pot and need to flush it, you need to use 10 gallons of water to rinse out the soil good enough to get rid of excessive nutrients. Soluble nitrogen (especially nitrate) is the form that’s the most quickly available to the roots, while insoluble N (like urea) first needs to be broken down by microbes in the soil before the roots can absorb it.
Note: Blood Meal, Dried Blood, Guanos, Kelp Meal, Cotton Seed Meal, Peat Moss, Sulfur and fish meal are all acidic and can bring your ph down, so if you add these please monitor your ph when using those.
Note: Bone Meal, Rock Phosphate, Wood Ashes pretty much all ashes, Shellfish Compost and Crab Meal are all alkaline and can make your ph go up, so if you add any of these please monitor your ph.
Here are 3 pics of what a nitrogen def looks like… the first one is a nitrogen deficiency in vegging. the 2nd picture is nitrogen def in flowering; THis is completely normal for mid to late flowering; as you would want your plant to naturally yellow at the end. DO NOT add nitrogen supplement to fix the problem; just let the plant yellow as cannabis does towards the end of flowering. The last picture is one that is caused by TO MUCH Nitrogen.
Hope this helped