Lower fans have brown splotches.

either you spilled nutrients on the leaves or it's cal/mag/iron deficient. pull super dead leaves and give some cal/mag/iron. coco sucks iron up so you have to supplement lots of cal/mag/iron in my experience. nothing to worry about.

Calcium deficiencies are more likely to appear when… Grower is using filtered or reverse osmisis (RO) water to feed plants – the amount of calcium found in tap water varies, but some tap water has enough calcium to prevent calcium deficiencies PH is Too Low – If grow medium is acidic (below 6.2 pH, Calcium can get locked out even if the Calcium is physically there) Growing cannabis in hydroponics or coco coir without supplementing extra Calcium (it’s recommended to use a Calcium supplement in hydro or coco) When growing in soil that hasn’t been supplemented with calcium (usually from dolomite lime) Too much potassium can also sometimes cause the appearance of a calcium deficiency Solution For Calcium Deficiency In soil, calcium is best absorbed by the roots in the 6.2 – 7.0 pH range (in soil, it’s generally recommended to keep the pH between 6.0 – 7.0, but calcium specifically tends to be best absorbed above 6.2) In hydro, calcium is best absorbed by the roots in the 6.2 – 6.5 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but calcium specifically tends to be best absorbed above 6.2) If you suspect your growing cannabis plant has a calcium deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes calcium. This will remove any nutrient salts that may be affected the uptake of calcium and help restore pH to the proper levels. After a calcium deficiency is cleared up, the problem (brown spots and unhealthy new leaves) will stop appearing on new growth, usually within a week. Please note that leaves which have been damaged by a calcium deficiency will probably not recover or turn green, so you want to pay attention to new growth for signs of recovery. To supplement with extra Calcium… (it’s very rare to give a cannabis plant too much calcium, however, too much calcium can lock out other nutrients so don’t go overboard) Calcium and magnesium deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case this common deficiency appears. Listed below are common cannabis Calcium supplements, along with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy. How to Use Dolomite Lime for Cannabis: When growing cannabis indoors, add 6-7 teaspoons of fine dolomite lime to each gallon’s worth of soil. So if you’re mixing enough soil to fill a 5 gallon container, you want to add 30-35 teaspoons (about 2/3 cup) of dolomite lime to the mix. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with water that has been pH’ed to 6.5. After getting the soil wet, mix the soil well and wait a day or two to let the soil settle before checking the pH and adding plants. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.

Hi mate, It looks like a calcium deficiency. You should give them a meal with calmag and see the response.