I purchased 4 new bulbs from a vendor here in Sep 2009. Two months later one bulb died; I contacted the vendor who gave me the manufacturer email and number. They replaced the bulb with no problems. I noticed today that another bulb is now out which is why I think the bubble algae is starting up heavy. My question is how can I determine if its the fixture or the bulbs? It is a 36" Tek T5 4 bulb with individual reflectors.