calcium deficiency?

Thanks guys, I will try and add some more X to the feeding. perhaps it comes from the coco coir which I didn't prepare and buffed correctly. I did feed the FB from day one though. all and all they seem a bit small compared with others here, but they look healthy (except this one FB). I have got a hold of a Garden Sprayer Air Pressure to distribute the feeding more evenly. it was also a problem I had. just poring in the feeding left the surface unevenly wet.

Could be due to the root zone not wetting everywhere after watering. Those felt planters arent the best for getting the entire medium wet so you need some extra water when you water. Cheers