Guppies dying
 

I have 2 otocinclus in a 5 gallon tank that are doing well. I had 3 male guppies in too, but 2 of them have died already in a 2 day period. I added salt to the aquarium some time before I put them in. Why would 2 out of 3 die? I'm keeping an eye on the last one to see what he does.

could be to stressed, also if you have that many fish you should definetly think about upgrading to a ten gallon because that is the minumum for guppys, here is a good site to look at the tank size for fish, how big they get so you will know next time,,, www.fishlore.com

First off, Otocinclus don't do well with salt. I would test the water or have it tested at fish store to see if parameters are within safe levels.

What would be a good collection of fish for a 5 gallon aquarium?

Were it me . I would put no more than five male guppies or no more than six neon tetras, or no more than six sparkling gouramis,no more than five forktail rainbows, no more than six Endlers livebearers or no more than one betta.

A betta is perfect for a 5 gallon... I don't know about 5 guppies in a 5 gallon though, thats a little packed IMO.