zoom in closer, I can't really see it that well from here. Make sure the colony is getting plenty of flow. Fungal infections are not uncommon and can be treatable if caught in time. I doubt their too close to the light, I have a colony about 6" underneath a 6 x 54watt HO T5 fixture. Their happy. And their sister colony is in another tank under normal output bulbs and they look just as fabulous, only not as bright green.