There are lost of protein skimmer on the market and it can become hard to make your choice.
There are pretty huge skimmer that can handle more than a thousand gallons of water.
But you can have a small one for a 10 gallons aquarium.
You will have to look through the specifications of the skimmer.
You need to choose one that can handle twice the water for your tank, If your aquarium is 20 gallons, you should pick the skimmer that can handle a 40 gallons tank.
This is important cause you don't want to finally have a skimmer that can't handle the life in your tank.
There are 3 types of skimmers: hang-on, in-sump and in-tank.
If you plan to make a big tank and you have a sump under it, you should go for a big skimmer that can fit in the sump.
That way you won't see it in and around your tank.
The hang-on skimmer is a great choice if you don't have a sump.
There are skimmer that fits inside your tank, but you always see it and it's not the nicest display.
A skimmer is the filtration system for saltwater thanks.
You don't need any other filtration system.
The only other filtration system that is allowed is a sump or a hang-on tank sump where you use special algae to purify the water.
Skimmers can be very expensive.
The higher you pay for one, the best quality you are supposed to get.
So check online, read reviews about the model you are interested in and if everything looks fine, buy it.
It will be a nice addition to your thank and your fishes will thank you for the pure water.