"Sarah" wrote in message
...
Anyone know when a Hagen Aquaglo tube should be replaced?

The website claims a life of 7500 hrs, so when the tube is used 14 hrs a
day
would be a life of around 18 months.

Some research on the net suggests that the output of the tube rapidily
decreases with age for some tubes, some tubes however (such as the triton)
run at near full output untill they fail.

Does anyone know which theory applies to the Hagen Aquaglo?

I'd say 9-12 months myself - I think your guess is as good as anybody's!
Their "Life-glo" bulbs are supposed to last longer (but are more expensive -
that said they do work very well).