Giving CalMag but getting magnesium-deficiency?

That's not Mg deficiency. Mg deficiency takes 30-35 days from the point of not having enough inside the plant to the point at which you see symptoms. The symptoms are intervienal chlorosis with spots. got some clawing at end of leaves, which is an indication of something being fed at too high of levels. Grow lights make plants look pale even if they have a healthy lush color. Either turn down grow light or if you take a leaf off (that needs to be removed not whimsically so) look at it under normal lighting and re-assess the color. You need a certain level of N/p/k/ca/mg/s at all times with some variations due to stage of life. Ca can lock other stuff out but you'd see obvious symptoms. See mulder's chart for what it can lockout, potentially. You should be adding calcium and magnesium and all the other elements if the soil does not provide it. it needs all of these nutes and secondary nutes and macronutes at all times one way or another... it's not a sometimes it needs caclium sometimes it doesn't thing. The levels it needs may vary, but it always needs these nutes. you've got a hint of interveinal chlorosis starting. This could be caused by several things. At this point it is impossible to know what it is just from leaf symptoms. If in a soilless/hydro context if providing 75-ish ppm of Mg, it's most likely not Mg. If not giving some insane ppm level of Ca, probably 150-200?, it's probably not Ca locking stuff out. These are values calculated from gauranteed analysis labels and not some shitty TDS pen converting EC in some whimsical way (4 different conversion factors are used depending onthe TDS pen manufacturer). interveinal chlorosis is not a discrete symptom. I'd suggest waiting a bit longer before reacting. e.g. if damage froms on the serated tips, it's pointing at low K, which could look like this at this extremely early stage of symptoms. if in soilless, calculate ppms of what you provide. when something is too low or high it sticks out like a sore thumb. free apps can tabulate the ppms per molecules for you.. just type in info off labels and dosing. if in soil, it's not as easy to get the balance right for your plants. There are intermediary steps that dictate rate at which some nutes become available to the plant, and that must be considered. It's less math and more trial and error, so it takes longer to figure out and you rely more on the indiscrete symptoms you can see then hope for the best after you adjust. lol, 6.5ish is fine... ish merely means a small range and that's all you can expect anyway. 6.3-6.8 is fine for soil and will not be the cause of any problems. it is a log-scale, but a couple tenths either way is irrelevant around 6.5... if approaching 5.5-5.8, all of a suddena couple tenths below can cause major issues. Probably have to go over 7.5 to cause issues in the other direction.