close to end, BUT WHAT IS THIS?

i'm 40 days into flower and this shows up.
she is blimburn acapol gold.
being in with 8-ball kush and mango ladies.
one with pipe cleaner is mango.
is this a mag problem?

What type of lighting? I see one that looks like a CFL but not sure...

Oh, and at 40 days, you are no where close to the end with Acapulco Gold .

What nutrients are you using?
i can clearly see burnt tips and the yellowing is because it has too much nutrients not too little, i say give it straight water for a week if its not time-releasd nutrients.
You didnt ask this but like brotherjericho said these plants arent even near done and that lamp doesnt look like anything i would be flowering under.

Hope you find the sollution soon
Peace

Looks like light burn/bleaching as the top is extra burnt.

^^ That's why I asked about the lighting, looks like what I get sometimes (just not as bad!) on particular strains under my LED panel. I typically have no issues with sativas, but many indicas cannot take the LED within a certain distance.