Hey there,
I like to swim and I like to try out public baths in vienna so I will introduce you some. The city of Vienna provides an overview here: https://www.wien.gv.at/english/leisure/bath/bathlist.htm
Source: CC BY-ND 2.0@H.KoPP
Today I will show you my favorite bath, the Amalienbad. I love it because of the wonderful architecture which has been built between 1923 to 1926 from Karl Schmalhofer and Otto Nadel. The pool has 33,33 m which is quite nice in Vienna. Next to the main pool there is a small pool where you can relax. The bath is next to the underground station Reumannplatz of the red line U1. You can find the terms here in German. When you go to google maps and type in Amalienbad you can find out how many people are in the bath:
At the moment (01/2018) a ticket costs 5.9€ for an adult and 4,40€ for 2.5 hours. You can find the prices here in German.
So if you want to swim in Vienna and you don't need to have a 50m pool (Stadthallenbad) this is quite a nice place I can recommend. If you visit Vienna, like public baths and stay here for some days I can also recommend to visits baths in Budapest which you can reach by train for 20-40€ in about 2.5 hours.