I would like to offer some humble advice, because I believe I had the same problems as you. You have/had the start of a magnesium deficiency, typical of coco. My solution so far has been to feed stronger and earlier, and to add some epsom salt (about 1 gram per gallon of water). The problem is most people will recommend adding
calmag. I'm using 2 part Megacrop (basically a clone of Jacks), which already has a good amount of calcium in it. Using
calmag to fix the magnesium deficiency also gave my plants excess calcium, which then caused a potassium deficiency. I incorrectly diagnosed the potassium deficiency as nutrient burn and was scared to increase the EC high enough to get healthy green leaves. I ended up with light green plants and deficiencies until a few weeks into veg, at which point I had slowly raised the EC as the plants grew bigger. Since I switched from
calmag to epsom salt I have had zero magnesium deficiencies. My plants have never been healthier or happier.
Also if your water is over say .3 EC it doesn't leave you enough room for your nutrient mix while staying within reasonable EC. You discovered this with your .7 EC water taking up most of your overall EC. I use one of these cheap "AQUATICLIFE RO Buddie" RO filters from Amazon. It will last a very long time for a 4 plant grow without needing replacement filters. I've been using mine for about 4 grows now on the original filters, and I use it to fill jugs for drinking water too. I have the 100 gpd one and it can make 5 gallons of RO in less than an hour. You can connect it to your kitchen sink, hose faucet, etc. They make a 50 gallon per day one that's cheaper, too.
Otherwise your plants look really good. Don't overthink things too much. Keep your VPD correct, keep up indirect airflow, and you won't have to worry about too much else. If you see magnesium deficiencies, treat it with epsom salt, unless you actually see signs of a calcium deficiency as well.