Are protein skimmers necessary in a 40g???

So I've been reading some old random threads and seeing a lot about protein skimmers and sumps. I've had my tank up and running with fish and a few corals. Probably 50 pounds of rock or so. Tons of great growth. It's been going for about a year and a half with no issues. I do not have a protein skimmer and have never had anybody tell me I should have one. I also just have a hob filter. No sump. I was under the impression in order to have a sump you need a tank that was made for a sump with predrilled holes.



Can someone clear this up for me. And if I do get a skimmer where would it even go?? No room on the back of the tank but I don't know how they work.



I've just done my weekly water changes snd monthly filter cleans. I've had a couple issues with algae but nothing serious.



Any advice is greatly appreciated.

Thanks