I just bought a SunSun HW -302 canister filter from EBay. This is my first time buying and using one. I'm adding it to my 55 gallon tank that already has an hanging filter on it. My question is when opening the box to put the canister filter together.i found out from reading the manual this model did not come with a uv
light. It does not even come with a switch to run one off or on. I found out I can buy and add one on. What does a uv
light do and do I really need it for my gold fish tank? I'm so new to this back than you just toss a fish in a bowl andbthats it lol..also looking at YouTube videos some people use lava rock in stead of the bio balls I'm confused about what is what and what to use can some one break this down for me it's enough to make my head hurt.