Keith Moore wrote:

Fluorescent bulbs absolutely grow dimmer over time and problems can arise from
diminished output, such as increased algae and poor plant growth.
It just doesn't make sense to replace a CF bulb that is performing well.

Keith, here it is from another perspective: You spent good cash to purchase a CF
system, probably 4X-5X what an adequate Home Depot shop light system would have
cost. If you weren't concerned with light quality and output, you certainly would
have saved those funds, or invested them in another purchase you valued more
highly.

At this time, you are NOT getting what you paid for. If you are OK with this,
great, although, the obvious question of why you invested in CF in the first place
does arise.

If you want to get what you paid for, and what you enjoyed for the first 18
months, replace the bulbs. That's my thinking, anyway.