+1 very good advice.Your fish has ich.
I will say one thing I have learned about ich over the years.
Ich is highly contagious... But only if your fish are not healthy, or are stressed out. I have treated ich, inside a fully stocked tank, with only one fish who caught it. That one fish only caught it because I was dumb and didn't use a quarantine tank and it was a new addition. When I treat ich, since I know all my fish are healthy, all I do is crank up the temperature and let it burn through its life cycle faster.
When I was young I had dirty tanks with bad water quality and many times when I had a fish that caught ich I would lose multiple fish to it in the end, even using meds. Now a days having ich doesn't bother me a bit. I'm serious when I say a healthy fish just doesn't catch ich, their immune system will stop it.
I'm telling you this because I basically want you to know don't panic. If you have cared well for your fish up to this point it isn't going to be a big deal. If you do indeed have healthy fish I highly recommend going the no medication method. Use some heat, and if you so choose aquarium salt. Crank the heat to around 86, your fish will get worse for a few days then suddenly be 100x better after about 5 days. During that time feed them well and keep the water clean, and everything should be easy.
If your fish are not healthy or you have your doubts, go with the meds suggested above.
Vacuum good too in hopes of catching cysts that have fallen off and not hatched yet.