All my fish keep dying

Ala2382

In Sept I got a 10 gallon freshwater tank. We had 7 fish, various tetras. The fish did really good! After about 2 months we lost 1 fish every couple days. All the fish died except for 1 and a scum sucker. I found it very odd. A couple weeks went by and my 1 remaining fish was still alive. So i went and got 4 new fish to add to the tank. I brought them home and did the acclamation process and added them to the tank. In about 30 minutes 3 of the new fish were dead. The fourth one lived until the next morning and then died. So i was convinced that something was wrong with the tank. I tested the water and all level were perfect! I could not find anything wrong with anything. All thw while i still have the one original fish alive and thriving. So i got 4 more fish a couple days later and the same thing happened. All 4 new fish were dead within an hour of introducing them to the tank. I have no idea what is going on?? I'm so confused because i have this one fish that is one of the original fish and is doing great! Does anybody have any ideaa or suggestions? I really love my tank and would like to get more fish.

AndrewM21

Could you please provide your readings? Also, how did you test it, strip or liquid kit?

pH
Nitrate
Nitrite
Ammonia

Water Temp

Frequency of water changes / How much changed

Did your fish have any abnormal markings pointing to an infection/illness?

djembekah

also, what type of tetras were they? and what is the "scum sucker"

Byron

We will need a lot more data, including that already asked for (which will be repeated below), in order to resolve this.

How did you cycle the tank when you set it up?
Which fish species were originally acquired and how many of each?
How were they (and subsequent fish) acclimated?
How often do you feed, and what foods and how much?
How often do you do a partial water change, and how much of the tank?
What is your water conditioner?
Any other substances/additives going in the tank water?
Live plants?

Water parameters (tap water)--you can likely get these from the water supply people's website:
What is the GH (general hardness)?
What is the KH (carbonate hardness or Alkalinity)?
What is the pH?

Tank water:
What is the pH?
Ammonia, nitrite?
Nitrates?
Temperature?

Before they began dying, did you observe any abnormal behaviours?
Was there any sign of bullying/aggression?

Byron.

FranksTanks

Once you get Byrons questions answered, the answers will flow....

One thing to keep in mind also, is that many fish are "schooling" fish, which means you need to have at least 6 of the same fish. From the sounds of it, you had one each of different kinds, is that right?

If so, that can cause a lot of stress with your fish, because they will tend to be more aggressive since they can not school. Just a thought...