I just purchased a used Expobar Office Pulser it came with a very strong smell fish tank or algae smell. What does that mean and how do I get rid of the smell? The water passes through the machine with no trouble and is clear when it comes out.
You've got colonies (of bacteria, and perhaps algae.)
I'd be looking for something a bit stronger than vinegar or citric acid in the sanitizing line, though either of those might be a good place to start, just to clear out any calcium deposits that other things might be using as a growth substrate (attaching to.)
Depending on your preferences, and/or any information you can find about what is recommended for your machine, this might be bleach and water, or one of several choices from the (beer) brewing products such as PBW (powdered brewery wash), Star-san, or Idophor. Star-san (at least) will also attack calcium deposits (it's mostly phosphoric acid.)
Rinse well, many times, when done.
I personally would check the brewchamber to see if there is any old water buildup that could possibly be getting moldy. I know nothing of the Expobar Office Pulse machine, but if a water intake is being used, check that pump and valve as well. or just run a vinegar solution through it if you have access to where the water in slowing into the machine.