What medium are you in? If soil-less, do a medium pH test, and a runoff test.
If you runoff is coming out higher than what you put in (say you put in 500ppm, and it comes out 1200, you are either overfeeding, or it is locked out due to pH swing and salt buildup..
Every time I've had yellowing/burn, you can guarantee the runoff is coming out higher than what's going in. For example, I have two autos in a 2x4, one was showing minor burnt tips so I checked runoff. The plant with no issues went in at pH 6.1 and 800ppm, came out at 6.0 and 835ppm. The plant with slight nutrient burn went in a ph6.1 and 800ppm, came out pH 5.7 and 1180ppm.
I fed at 300ppm of base nutes for a few days, went back to 800ppm and the runoff now comes out as 730ppm and pH 6.0. the burn won't fix itself, but the new growth is darker within a few days.
Monitoring pH and ppm is probably the best way of keeping track of how the plant feeds. It's good to keep a track of metabolic cycle. The runoff will let you know if it's feeding, or slowing down. .if the ppm comes out considerably lower, you can safely up the feed, if it comes out higher, back off until it stabilises.
