I’ve had these two aquariums going since October. They have just had a beta fish and some suckers in it. Everything has been fine I’ve finally decided to get new fish yesterday. I bought 5 guppies for one tank And 2 angel & 5 tetra’s for the other tank they were separated into 2 different bags per tank to make life easier. They were not all in the same tank at the pet store but right next to each other. The tetra and angels were all in one tank and the guppies were in another. Fast forward I get home I let the bags sit for 30 mins I added a bit of water waited another 15 mins then poured them all in no issues anywhere. I wake up in the am the angel is stuck to the filter and dead no other fish appear sick weak or dead in either tank. So what could have gone wrong? Is it just simply bad stock? I’m going to take the dead angel back to the pet supplies and a water sample they will replace it they said. But I doubt it’s my water really it died really too soon. It’s been 16hrs. Thanks for any help!. These are two 10 gallon tanks I forgot to mention. Does not seem over crowded.