My pool light went out yesterday and I need to replace it. It' a 500 Watt flood light that I bought at the pool store maybe 4 years ago. At that time I was on Bacquacil and when I opened the light cavity it was full of white slim. This time when I opened it it was pretty clean with the exception of some white calcium deposits. I vacuumed out the cavity and now need to replace the bulb. Is this a special bulb for pools and can only be purchased from them? Or is this the same as any 500 Watt flood light that I could buy at Home Depot. The pool store wants $35 for this bulb. Also could the calcium deposits that are around the ground screw at the back of the underwater housing be the cause of the light not coming on? The bulb looks real good but I can't tell if it is broken inside.