Magnesium deficiency? Pics, please help!!

DWC with top feed
PH 5.8-6.2
400W MH 24 hr.
Flora Nova Nutes
Temp 79-81
RH 47-53
21 Day Veg

I started noticing the yellowing tips about a week ago, i added 10 tbsp of Epsom because i believed it to be a calcium or magnesium def. 2 days later i added 10 more tbsp per the 25 gallons, here are the pics any advice would be greatly appreciated!

Update* I did change the reservoir thats when i started to notice the change of color. Could it be Nutrient burn?

Looks like LOCKOUT of Iron or cal Or Mg

I figured that it was from when i changed the res, any advice on how to avoid it next change? Or how to fix the def now?

They are on the right track, im currently into week one flower and the problem was nute burn and lockout from the ph being off and adding the nutes directly to the res....i have been taking the top off completely and moving onto a second res, dry. topping off and keeping the nutes and ph sustained. Only problem that i think im going to run into is when i change and top off once they start growing taller, keeping them stable when removing the top...this is my first dwc any recommendations once they reach 4ft and are top heavy?