well, i will start by saying i run dwc, and if you want simplicity, the easiest route i found is to use maxigrow powder in veg. very inexpensive also. a 2.2lb bag will run you anywhere from 10-15 dollars depending on your source and if you get a discount.
use silica also to raise your ph, i used dutchmaster silica gold.
in a 5 gallon reservoir ( 5 gallons of ro water) i'd first add 9ml of silica in the first gallon i add, then add 3 teaspoons (scoop provided in the bag, the smaller scoop is the teaspoon obviously) of maxigrow. then add the last 3 gallons of ro water.. 3tsp in 5 gallons of water, and 9ml of DM silica gold.. then i'd have to add a few drops of AN ph down. but honestly it without ph down it targeted right at like 6.3ph, which is not horrible. you'll have the greenest healthiest plants you've ever had, and extremely inexpensive and easy to maintain. then just dump weekly and redo it. you can stretch to 2 weeks if you want during the first couple of weeks of veg. but the nutrients are so cheap, no need to.
don't be fooled by big price tags, salts are salts. and maxigrow is just as good as anything else, and way simpler.
3 tsp per 5 gallons puts the ec at around 1.2, and they will stay green at that level. i also recommend some sort of beneficial bacteria to keep root zone healthy, i don't like the sterile route. using microbial tea in your reservoir will allow you to run at higher temps, and also allow a slightly wider ph range of uptake.
and don't be fooled by the 'plants need more P and less N in flower' that everyone online is boasting.. its true they use more P than N in flower, but its in subtle amounts and you don't need to change what you're feeding the plant. a proper balanced ratio of nutrients is WAY more important than adding a PK boost. high P levels will hinder uptake of N, Ca, and Iron mainly.
you can run maxigrow alone all through veg and flower. i use it at the rate of 9tsp per 10 gallons of RO water in flower, 18ml of silica (always add silica alone and first), and then like a few drops of AN ph down. i like AN ph down cuz its very concentrated and only takes drops to work.
but if you're not sold on the idea that a higher n, lower p is the ideal ratio for cannabis, or any other plant (cuz it is fyi) they have maxibloom, which is just as cheap and just as easy to use. except you'll have to use PH up because its very acidic. I truly recommend, from personal experience, that you run maxigrow from start to harvest, and do like 3 days of unadjusted RO water only at the end.. i promise you'll have one of the best harvests you've ever had.
oh, but back to the original question, I have ONE strain (cherry pie) that no matter what i do to it in DWC, i always get those brown necrotic spots.. i can't prevent it. but it doesn't affect my harvest or quality. it happened when i ran maxibloom in flower.. i suspect it was from the high levels of P in relation to the amount of nitrogen, potassium and calcium.. which was causing a misbalance in the micro nutrients. but i could never narrow it down to what it was.
ive found that no nutrient line is perfect. the only way to truly dial things in is to buy the raw salts yourself and make your own nutrient formulation, which i am in the experimental stages of right now.
but yes those pics def look like early calcium deficiency.. if you run maxigrow i never had any calcium deficiencies when with RO water on any strain.
