28 Gallon skimmer
 

I was told by my local saltwater aquarium store that since my tank is 28 gallons and I plan on doing weekly water changes, that a protien skimmer would not beneifit me. Is this true? Is it necessary for my tank? I also have a very nice glass top on it and I can only cut away a couple inches to even fit something into the tank such as a skimmer. Any ideas?

I have made a DIY protein skimmer on my 25 gallon and it is pulling out skimmate like nobody's business. I think only very tiny nanos such as 10 gallons or below don't need a skimmer, but you definitely need one.
If you are cheap, you can DIY one with an airstone or a maxijet mesh mod. Search those up. And basically a DIY one: is a long tube with the bubbles source from the bottom and it narrows into a collection cup. Its quite easy to make, you can even use one of those gravel siphons to make a nice once. Make sure you haves some epoxy and silicone though.
good intank ones are the biocube protein skimmer, the aquaticlife internal mini, or the hydro slim

like everyone, i would recommend a HOB one...something like an aqua C remora, reef octopus...

Depending on your bioload, you may not NEED one, but you definitely should have one.
If you have corals skimmer is a good idea
lots of fishes will def need skimmer

my 2 cents.

*also with a skimmer you can do a water change every other week. I am wayyy to lazy and i have some pretty interesting chemical filtration (purigen, chemipure, phosphate remover, polyfilter, carbon) and skimmer running, i do like a water change a month. My parameters are fine. The skimmer will allow you to do less water changes and save you a lot on salt. It pays for itself!

awesome. I will look into getting one. I appreciate the advice!