I purchased some T-5s from Marine Depot a few months back. My Giesmann Pure Actinic went out yesterday. I Emailed them thinking these should last a bit longer. They said they would prorate the warranty. Since the shipping of one bulb is a pain in the rear, I asked them if they would wave the shipping If If I bought 4 more bulbs. They agreed and so I bought 4 more T-5s.
I thought that was nice of them to do. I think they charge more for shipping bulbs that are 48 inches and must be at least for bulbs.