bert, why do you ask for help then ignore it? wtf? Anyway, I am patient and will give it one last shot. FOCUS! You are definately over watering those plants flooding them several times a day. The root system is small, I know this because not much is happening up top, simple.
3ml per liter is 1/2 strength ionic dose which is 12ml per gallon @ 4L=1 gallon (check this as imperial and us gallons are different). 3ml is about 1 tsp, I just went and measured it. so.... from the above formula providing that 4l= 1 gallon I would give them 4 tsp per gallon 1/2 dose. I looked at a bottle of Ionic grow this very afternoon with you in mind. Our instructions say 7 ml per liter which is 2 and a bit teaspoons per liter, which works out at 9ish tsp per gallon full strength. Do you think something got lost in translation? Can you get a liter measure and a ml syringe to do your mixing? Maybe they printed the labels wrong, it has happened before although not with gt that i am aware. You want 4tsp gallon ½ strength, 9 tsp gallon full strength. Is this how you interpret the instructions on the bottle? If not I would email growth technology and find out what gives BEFORE YOU DO ANYTHING ELSE. Something aint right here, it looks like they either changed the strength for the n/American market or they fucked up their math. If it is the latter, this would likely be why you are having problems and why nobody else uses it over there!

Want to try an experiment?
I would try hand watering your worst plant around the rockwool when the rockwool dries out a bit, once a day? with 4 tsp per gallon I /G = (1/2 strength according to uk instructions), ph 5.7- 6ish and see if it bursts into life after a week. I am betting it will.

I have a few more thoughts but would like to get to the bottom of this first. Let me know how you get on.

Subzero. :thumbsup: