Maybe you all know this already but this is the first time I noticed. About 3 weeks ago, one of my tank that use ODNO fixture started to grow green algae on the glass (more than usual). After that, the following week, I noticed that all my plants didn't grow as fast as they did. My rotala literally stopped growing. Hairgrass started to grow taller than usual. I checked all the parameters and all were fine. Picked up the light fixture and found out that the 9325 bulb is noticeably dimmer (8 months old-5months overdrived). I switched to new bulbs and everything went back to normal. The funny thing was that it's a 6wpg tank and one dimmer bulb wouldn't make it less than 3wpg. But somehow the plants wouldn't take it.
Well, I've never notice how important it is to change bulbs until now. Maybe the overdriven fixture make it more obvious (sudden drop of lumens also I guess instead of spectrum shift). So for you guys who suddenly have problem with your tank, don't forget to check your bulbs. Maybe it's time for new ones
For those who don't believe in bulbs usefulness lifespan, good luck to you because I wouldn't take that risk.