Mg deficiency first appears as a yellowing around your leaf margins / edges. More severe deficiencies produce a deeper yellowing.
Common symptoms include
1. Yellowing of the foliage - Interveinal chlorotic mottling. The leaf veins remain green while leaf margins are pale yellow or even off white.
2. Leaf Curl
3. Premature drooping and dropping of older leaves
4. Poorly formed buds - Flower and fruit production requires progressively elevated levels of magnesium as the plant approaches maturation and harvest.
5.Poor tasting sometimes bitter fruits or edible leaves and foliage - In mild cases of Mg deficiency plants produce small, fibrous and woody fruits.
6. Stunted growth
The most obvious cause of a magnesium deficiency is that you simply do not have enough magnesium in your solution - elementary. Adding Epsom Salts is a quick and easy remedy. See: Epsom Salts for Hydroponics.
Unfortunately it's not always as simple as all that, in many situations there is ample Mg in the solution but other issues prevent its uptake by the plants.
High pH - a nutrient ph above 6.9 will prevent your plants from up-taking adequate magnesium. Even though your nutrient solution may have the correct content, your plants will be unable to absorb it. In severe cases it may become necessary to flush your solution and start again, before doing that however you can try using pH down / phosphoric acid to adjust the pH to the correct parameters.
Calcium and Magnesium deficiencies commonly occur simultaneously and have the same root issue Nutrient pH. Calcium deficiency, like magnesium is more apt to occur under an acidic pH [high]. In Hydroponics, calcium is best taken in by the roots in the pH range of 6.2 - 6.5. Once you go too far above that Calcium absorption is hampered. So if you have a high pH and a deficiency of Calcium and Magnesium than obviously you have found the issue.
If you do not have a high pH add a suitable Nutrient formula for the crop being grown. As Calcium and Magnesium deficiencies commonly occur simultaneously it is advisable to supplement your solution with calcium and magnesium [Cal-Mag]
If you have Excessive Calcium, it will hamper not only the uptake of magnesium but effects other nutrient availability as well. Nitrogen, phosphorus, iron, and potassium and some trace elements will not find their way to the plant tissues if calcium is in excess. Catch 22- Calcium and Magnesium deficiencies commonly occur simultaneously - so obviously if you have a calcium deficiency - excess calcium is not the problem. See: Hydroponic Calcium.
Excessive potassium will also hamper magnesium uptake. If the plant is taking up too much potassium one of the first symptoms to appear will be a magnesium deficiency in the older leaves towards the plants bottom.
Excessive sulfur affects the way your plant metabolizes magnesium, although this is rarely an issue. With excess sulfur or sulfur toxicity the leaf will appear yellowed and scorched near the edges. Leaf size will also be diminished and overall plant growth stunted.
Hydroponic Phosphorous Hydroponic Nutrients pH in Hydroponics
Thank You and Happy Gardening.