Does rapid growth=healthy plant

I am growing in coco/perlite and using gh flora series plus calmag. My plants are15 days old today and are rapidly growing at this point. Doubled in width in last 36 hours. Wouldn't grow this fast if unhealthy I would assume. I ph my water and alternate between plain water and nutes. My plants due appear to be stressed and have some yellow burnt tips and what not. I thought I had burned them with nutes last week but am unsure what the problem is at this point. The rapid growth in width mostly leads to believe they are relatively healthy. The discoloring began last weds so I flushed and just reintroduced nutes yesterday. The condition was slowed but has continued tho.This is my first grow by the way.

Here are pics by the way, this plant is becoming a monster. Just want to keep it alive. The stalk is the size of my pinky finger. Maybe this is normal but being a noobie I wouldn't know.

Rapid growth could be due to nitrogen. My oppinion

Yeah maybe so, they really exploded after I reintroduced nutes. The dead spots forming randomly concern me tho. There are signs of it starting on new growth also. I'm going to start flowering next week and need a good week of growth with no problems.

Any thoughts on what my problem might be would be appreciated.

Are those bottom leaves touching the soil?

No they are not

Wow, monster,,,,lol

New to this eh?

"Burnt" tips means you need to lower the amount of nutes you use a bit.....as the plant grows it will need more but right now your too concentrated for the size of the plant.

A monster for 2 weeks old, I know they get very large. And yes, I'm new. Lol