Nutrient lock out

I don't know what a ppt is, I can only assume you mean ppm. However of 700 scale or 500 is another question.
First off.... Lock out which I don't know that you have here, I believe you have a high pH, low ppm issue and she's hungry as F. And yah definitely could use some major cal mag, seeing as how the upper part is yellowing, it says it's not a mobile nutrient. More likes calcium and iron, IMO.
Anyways "lock out" can happen without a plant there- but that's besides the point. Or is it... Anyways
How are you feeding/watering her? How often? What are you feeding her?

 

U got enough light?

 

I stand by my original thought- high pH and not enough food.
I was taught 6.2 is optimal pH to aim for.
I don't see this burn, your referring to.
If you convert 1.5 ppt to ppm it's like 0.0000015 or something. That's like no food.
So if your feeding 250ppm, and it's flushing 0.0000015, that means it's has eaten almost everything, well 249.9999985 of what you put in.
I just see a hungry girl.
Best of luck.
Beautiful last plant you had there.

 

this plant should be feed around 500 ppm

 

this one 250 ppm

 

that is a age old clue,to tell you that you gave to much mate,most likely if you continue to force feed the plant it will even get bigger,when it starts to wrap around all your edges of leaves you have way over done it.
but from what i see you just tickled her ,those tip are just barely visable ,so that is your sign of to much but not that bad,
it is rare that i dont see tip burn from nutes,it wont hurt nothing but you just dont like it , i dont anyway,follow the hannah feed chart and you will do fine mate,you hear force this and that all the time,the plant only takes what it needs not what you think it wants,so you wind up with the burn, all this said the baby i would continue at 250 until it gets 3 sets of full leaves and bump it up 50 ppm more,but honestly the chart even say to extend the levels more in flower ,i dont,i dont go over 900 950 max.
why you thinking,because that about the time you start watching the thrics and reading for harvest,less nutes less flush.
i even take it a step further,when i see the very first cloudy thric i start feeding backwards ,so if 900 i start moving back down slowly to the 250 i started with,that will make the plant eat all that it is retaining and just die,less time curing and drying also

 

are you using the 500 or 700 scale,im talking about the 500 scale

 

main thing to do is,go by EC it is same on which ever scale you have,the chart i sent was on the 500 scale,again 500 or 700 the EC is the same