Lloydlost

Thankyou so much for replying I did all the above,,,is there a reason why the older fry died and not the younger ones?

I've been raising a batch of 40+ gardneri fry in bucket outside. Today I noticed them gasping for air and on closer inspection I saw most of the fry that were 1inch and above were either struggling or already dead. The water was smelling really bad as well. The bucket had no air, it was outside, and had a plenty of guppy grass. Over the past 11 days ive been away and my mom has been feeding them, also the top was covered with duckweed. I know it's a terrible situation but any insights to save the rest of the fry would be helpful