Missing & Dead Neon Tetras - New Tank

Oh, just to add..ph usually is not a huge deal, most fish adapt..but both cory cats and cardinal tetras need a lower ph than what you have..I keep mine at much lower than 8
 
Neons can be surprisingly good at hiding. I have a five gallon tank that one hid in for about two months. He was just there one day.

They sometimes jump too. I have the baked remains of won inside the light shield of said five gallon.
 
Waiting a week could have killed off much of your bacteria in the rocks and media..

I am sure some bacteria was left, but not enough to handle several fish. If you added a fish a week you probably would have had better luck.

I hate undergravel filters :)

Cory cats can be very sensitive, but they are pretty hardy...please try a water change.

edit to add...and do a good vacuum to bring those nitrates down
a week wont adversely affect your bacteria.

nitrates arent unusually high, but it wouldnt hurt to lower them through water changes. with such few fish it seems like it has been a while since you have done water changes, sorry if i am wrong with that assumption.

OP:
do water changes.
use water conditioner.
do more water changes.

also find out what your ammonia readings are. most like your fish just happened to die. they do that sometimes for no reason.
 
I've done water changes every week. Ammonia went up to .25 ppm on Wednesday but I did a water change and no sign since. I now have one neon tetra left - one went dead//missing today, 3 Cory cats and I lost my betta today. I'm just sick about the betta - this whole tank was being set up for him- I've had him almost a year. Brought more water to LFS to confirm it looked ok- nitrates are closer to 10ppm now everything the same. The guy at the LFS thinks either second neon tetras had disease or the "feeder fish" petco convinced me to start the tank with had something. His guess is I'll lose the other tetra too but the corys may survive and said he doesn't think there is anything else I can do.

Now I have some weird stuff on my plants- starting new thread with pictures.
 
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