They are about 10 days old, I like to replace them about once ever 6 weeks. I know I spend a lot on doing that, but water needs to be clean in my book :)
I have 2x400 10K XM's with a IceCap 48 inch VHO Retrofit Kit 4 Lamp unit, and moon lights. The VHO comes on at 8:30 am then the 400's come on...