Leaves issue

Nutrition issue, nothing to do with "root rot". Start a diary and tell us exactly what you have been doing.

if properly buffered by the manufacturer, coco coir should not leach any Ca from nutes... that is a sign of a shittily manufactured batch of coco coir if it does. coco coir is dangerous if it is not properly processed for use with plants.

possibly too frequent with your irrigations. Hard to assess leaf color under grow lights. They always look paler than they actually are. is it paling from tip-in and bottom up (ignoring the necrotic bits)? If so, that's a sign of needing a bit more N. 120-130 ppm should be all you need of N. if it is from too frequent irrigations, just wait a bit longer between. I know cocoforcannibis says it should always stay wet, but that's retarded and too simplified. If it stays wet for too long it'll grow weird shit and you'll have root zone issues. "Always wet" also requires some minimum rate of drinking or it's going to cause a problem. in vege wait for top layer to at least start showing a little change in color. When it drinks down the pot in 2-3 days, can consider more frequent irrigations. Maybe daily at first, then if it's drinking down 25-33% of water weight, can do a 2nd one in same day, if you wanted. From what i've read, you don't get much ROI after 2-3 irrigations per day... and only if the plant size match pot size so that you don't get root rot or worse.

it looks like it wants more magnesium and nutrients in most pics but also showing a bit of burn. What are you feeding them? also have you been preemptively adding in CaMg with growing in coir? It needs this as the cation exchange sites will steal this from the plants and release sodium and potassium. Its hard to tell with no diary or other info but I don't think the main focus here should be just PH and PPM, Best to start a diary and add in as much information as you can on how they where grown.