Calcium magnesium deficiency reverse osmosis water

Hey everyone, These plants are 38 days flowering, I've set them up using a drip system w/ reverse osmosis water.
Was aware of the little trace elements of calcium and magnesium after filtration of R/O water, been using Cal mag where it states 1.5 to 1 ml per litre on bottle ,been using the latter.
Using bloombastic w/regular Bloom nutrients,soil is plagron batmix.
Grow set up in 2 metre tent,
I got 18 plants under two 1 metre parabolic reflectors Powered two 600 watt Sony Pia bulbs
6 inch intake 6 inch outtake.
I vegged these 18_19 days 16l fabric pots , not too far away from harvest ,says 50 days according to royal Queen seeds special Queen#1

I went into the Hydro shop today I ended up getting Epsom salts where I just used it as foliar spray..

Sorry about the lights on with the photos,
I did take some leafs off for better viewing, one of the plants had symptoms 10 days before the others not all the plants have signs counting 4 , it has been spreading slowly.
I know on my next soil Mix I will be using dolomite lime if I can get my hands on it would anybody knows something similar to dolomite lime,guy in the grow shop doesn't know of it..
Any ideas appreciated
Precautionary measures for the future

calcium def, get some liquid cal/mag it works much faster than dl

backtracker said:

calcium def, get some liquid cal/mag it works much faster than dl

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I've Been using Cal mag, double the dose so, I heard it's difficult to overfeed them CalMag. Thanks @backtracker .

Calcium moves slow. By the time it starts working you probably will already harvest but give gypsum a shot as a topdress.
I would not recommend dolomite as you don't want pH to change and you don't need anymore Magnesium by the looks of it IMO.

what is the new growth doing? that's what to watch the old leaves they tell you what has happened the new growth tells you what is happening. this late in flower be careful about loading up on ferts or your pot will taste like shit.