What is my deficiency?! I think potassium, but not...

Never done well with hydro myself but my buddy does and kept getting that same burn on leaf edges and always thought it was too much nutes but when he found out it was potassium defficiency he got some dutch master silica which is 0-0-2 and he said his plants grew faster and got much hardier like thicker main stems, stronger side branches on top of fixing the defficiency, which never even showed up on any of his grows since he got the silica. I noticed too when he started using that his leaves even felt healthier, like softer and less brittle but also a little thicker. I think it was like 15 or 20 bucks for a 1liter bottle at local brew and grow shop. Oh and because it raises ph he also never had to buy ph up again, just used a little of the silica. Plants still look great tho, hope its a good haverst for ya.