I have had a 90 litre aquarium since January this year. All was well until a few weeks ago when I bought five five, two of which died within 24 hours of putting them in my tank. Then my cardinals started disappearing (I assume dieing) until there were only two of the six left. When it appeared the tank was OK again, I bought another 12 neon tetras last week, and one or two have been disappearing each night. I have seen a couple of bodies on the bottom of the tank. I don't know if they are being attacked, or dieing. I have two angels and a golden gourami, but these are only small and until the introduction of the sick fish, I had no problems of this kind. Any suggestions?

Do you have a water testing kit? It would be very handy to know your ammonia, nitrite, nitrate, and pH readings, along with water temperature (if you have a thermometer and/or a heater).

My initial suspicion is you are adding WAY too many fish all at once, and that overload is flooding your tank with ammonia from things like decomposing poo and food and stuff. Neons are very delicate fish so many will perish without a trace (their bodies decompose THAT fast). In addition, all the unfound corpses are adding even more ammonia to your tank.

I would suggest an immediate 50% water change with a good gravel vacuum session, and dechlorinate the new water with some tap water conditioner.

In the future, add 3 fish or less per week, not 12 all at once. And I would advise quarantining the new fish if possible, to prevent them from getting any diseases they might have into your main tank. Also, read up on how to properly drip acclimate a fish (it's a sticky on this forum section), to significantly reduce stress on them from moves from the pet store to your house.

Welcome to the forum and the hobby!

__________________
Officially fishless until after the move....tune in later for details!

I had similiar problems in my tanks where there was not peat moss ing the substrate. But neons lived for years with peat.

I finally measured things and it turns out that Kh and GH both slowly rose to high values with just sand but stayed at lower values for years with the peat.

also make sure you check new neons for inflamed gills. I reject those at the store.


my .02

__________________
fw leiden since 1979, fo salt since 1979, mixed reef 55g 2002-2009. Strong emphasis on the tank taking care of itself. Balanced with plant life, no water changes, tap water, no filters in FW. Only dosing calcium, alk, mag in marine reef tanks. http://www.aquariumforum.com/f15/my-...ods-26410.html
recent tanks (till 2009) 7 years- 10g FW leiden 7 yrs, 55g mixed reef 7, 2 yrs, 20g FW leiden, 10 g fw leiden , 29g mixed reef, current tank 55g leiden

As a side note, tank is way too small for 1 Angel, much less 2.

Didn't you post this in another area? I'm pretty sure I responded to this question yesterday....

Angelfish need a 29g tank at the very least, so I'd either get a larger tank or re-home the Angels.

The Gold Gourami may also be the culprit, depending on his attitude...

Angels will eat any fish they can fit in their mouths.

__________________
20g Heavily Planted http://www.aquariumforum.com/gallery...00&ppuser=8981
36g Bow Front Heavily Planted http://www.aquariumforum.com/gallery...00&ppuser=8981

1 Angel can work in a 29g, but do something like plant the tank and even that is out. Angels "can" eat other fish....wrong to say they "will".

Sorry Ben. Correction: Angels 'can' eat other fish they can fit into their mouths - they are actually a type of Cichlid - but if they are 'easy going' or have been in the same tank as the smaller fish since they themselves were juveniles, they may not eat smaller fish.

__________________
20g Heavily Planted http://www.aquariumforum.com/gallery...00&ppuser=8981
36g Bow Front Heavily Planted http://www.aquariumforum.com/gallery...00&ppuser=8981