I have a light that has a cover over it(i think its florescent) it has one white light bulb(length of tank, and same one is purple and a moonlighting). Moonlights are tiny bulbs like 8 of them. And i want something that will show off theyre colors. can i change the bulb inside. I heard blue is a good one for tanks. i spent like 100$ FOR IT so i dont want to buy a new one but i might if i need to. And why do they have a purple light? why would i need purple?