Please help!!! Baby feminised blueberry going bad

Hi people i,m new to this and need some urgent help.

I first grew approx 5 years ago and had a great crop of white widow and sensi no1. Things are much different this time, I purchased 5 feminised blueberry, germinated 2 and they looked good but after two weeks all leaves went yellow and eventually died off, I put this mistake down to placing in nft tank far too early and also not allowing seedlings to become rootbound in rockwool before transplanting to system.Also ph to acid

I have restarted with two more both have really long spindly stems and growth is extrememly slow!!! They are nearly two weeks old now and have very small tiny sun leaves and do not look healthy at all, i have them in rockwool seedling cubes ph spot on half strength nutrient feed being fed. Also my system is 5 years old is it possible the bulb has no strength anymore, i only grew one crop with it, 250w hps bulb.

Please fellow herbs help i have seen other pics of lush healthy plants younger than mine, n i am looking at my plants n think they are lighting up in colour again. arghhhhhhh!:rastasmoke:

I was going to question the pH, but I see yours is already correct .. good luck