All 4 Neon Tetras died

WSammy

New Fish
Apr 18, 2016
4
0
1
#1
Hello! I came home today to find my 4 tetras dead today. All were fine last night. They were in different areas in the tank, except 2 which were stuck to the filter. What would cause them to all die together?

4 tetras (no longer)
3 male guppies
1 Otocinclus
10 gallons
73 degrees
Water tested normal last week, haven't tested since the deaths