They are not very new. Probably been in the tank for about 2-3 months now.
What I meant was that they were new to your tank/system 2-3 months ago. Then they were probably subject to light shock when they were moved from where you brought them. If that was during a period of very-low PO4, then that makes the light shock sort of a double-whammy on them.
These effects can be delayed to show up and can take months for them to recover from.
