Bloated zebra danios

[Kennakm]

Help! I had to be in the hospital for 6 days and just returned home to a relatively newly cycled tank. Its 10 gal, 5 zebra danios, 1 leapord danio, 2 guppies, 7 guppy fry. The nitrate levels were about 20ppm before a small water change and water levels were pretty low. Their light is automatic, and i had someone feeding them once daily (which is more than usual but i thought it might simplify). I gave them some frozen pea when i got home in case they were constipated or backed up. Well I’ve noticed one zebra danio is very bloated and not swimming much, and the others were fine but rapidly are acting sick, swimming or hovering in one place, all of them together.

Did i shock them or mess up somehow? Are they sick or just stressed?