different problems : please help !

Hello,
i have several plants in 3 hydro bubbler systems. In the same bubbler, i've got 5 little plants started from seeds. Only one is growing well, exept that the growth is quite slow imo. So on the same bubbler i can have one with yellow tips on the biggest leaves, one which leaves are curling strangely, one healthy, on the other bubbler, plants seem ok except the colour, very light green. I've no pics i'm sorry. I already experienced some ph problems, to high, but now it is stable to 6. I'm using GH flora series and i change nutes once a week. I use acid for aquariums to lower the PH. The root system is growing well imo. Just the plants don't look heathy and don't grow fast. Light is a 250 HPS now but i tryed fluoros and same problems. Temp is 26 celcius
Anyone can help ?
Thanks

In australia we have a disease that is called yellow sigatoga, dont know if you have it in the states, but thats what it sounds like to me, turn the leaves over and look at the under sides. Really need a picture to tell, hope you sought it out.