Are you using cal mag plus ? looks like a lack of one. What is your water temp? very important. A little h202 may help but sounds like warm rez. Change water a much as you can, 68 to 70 temp is beat for oxy. A closer look looks like your rockwool is dry and hydrotron rocks look dry too. If It's a bubbler you may want to bring your water level up and more bubbles if you can.
Give us a shot of roots.