Neon Tetras disappearing

Hi

I've had a male betta and 6 neon tetras in a 21Litre tank for around 6 months and everything has been fine. But a month ago one of the tetra's disappeared. No body, just vanished. I thought maybe the betta had eaten it, but he tends to ignore them. I did notice the other five were sparring a little, but nothing major.

Have just set up a 180Litre tank and have transferred them over. Also bought 5 more tetras. The day after I bought the 5 new tetras home, one is missing again. So now only have 9. Again, the betta tends to ignore them but really not sure if they are being eaten and if so, who's doing the eating? Worried that more will keep disappearing.

Any help with what to do?

Was also going to get some cardinals and red rasbora, plus a bristlenose, and a couple of discus. But don't want to do that until the existing fish are a little more settled.

 

I had that same problem only with DG’s. The betta probably ate the dead bodies of the neons. Neon tetras die all of the time and a 21 litre tank was too small for neons.

 

I'd have to say pass on the Discus. They should be in groups of 6+. Also, the absolute minimum tank size for six is 55 US gallons. They'd fare much better in 75 gallon or more.
Neon Tetras prefer a temp of 75f while Discus REQUIRE a temp of at least 80-85F.

 

I found my dead neon. It had jumped up between the glass lid and a perspex runner on the tank. Poor thing. But at least its not from aggressive fish, but an accident.

 

What are your readings for ammonia, nitrite and nitrate? Quite often, fish will jump to try to escape poor water conditions.

 

The readings are all fine, check them regularly and do regular pwc's weekly. Keep pretty on top of the water perameters, so def wasn't that.