My fish are dying :(

Question
QUESTION: Hello.  I've had a tank for about 2 years 8 months now.  About 2 1/2 months ago my betta died.  He seemed pretty healthy until he died on day.  He was the very first fish I got so I thought it might have been "his time".  He was in a tank with a rainbow fish, a molly, a platty and a tetra.  It's a 10 gallon tank.  Anyway, about a month later the rainbow fish died.  Was very healthy looking and eating seemed to just die suddenly.  He was the second fish I had gotten so again I thought it might have been his time.  Now my molly has died.  He was eating and swimming around the tank yesterday - this morning dead.  Coincidentally (or not) he was the third fish I added to the tank.  I don't know what's going on.  I clean the tank every Saturday and change the water (about 2 gallons).  All of the water parameters are excellent per my API master test kit.  I have looked up all the fish diseases I can find on the internet and they don't seem to be exhibiting symptoms of anything I can find.  The only change I made is that 7 months ago I moved to a new home which happens to have a water softener system, but if that were an issue I would expect it to affect all of the fish - not one at a time.  I know this problem could be very difficult to diagnose, but if you could help me at all I sure would appreciate it.  Thank you.  Rich

ANSWER: Rich,

I would say that most likely the Betta died from old age. They are usually around 1 year old when bought and most live 3 years or so so that sounds right. Some fish are more sensitive to their water conditions. When changing the water make sure you are vacuuming the gravel as well. Since they are not showing any symptoms it is difficult to try to figure out what happened. Make sure the food you are giving them has not expired. I am thinking there might be a water issue. Make sure the ammonia and nitrites are reading at zero and the nitrates are no higher than 20ppm. I would possibly do a larger water change and make sure the filter is clean and running properly. I would also check into the Ph and make sure it is right for the fish you have. Other than that, I do not see anything that you are overlooking and seem to be doing everything just right. I am curious as to the Ph level in the tank.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply.  I vacuum the gravel with every water change so I don't think there is an issue there.  I have live plants in the tank so there are some areas I can't get to, but I vacuum as much as I can.  I feed them New Life Spectrum Optimum flakes, but there is no expiration date on the container.  However, it's the food I bought when I first got the tank so I will get new food this weekend.  The ammonia and nitrites are at zero and my nitrates are at about 20ppm (although it could be slightly higher - sometimes hard to differentiate between colors on the card), but certainly no higher than 40ppm and as I understand it under 100ppm is a good level and I'm surely well below that.  I know the filter is running fine and is as clean as it should be.  I just measured the pH and it's at 7.4.  That's where it always is and has been.  I've never tried to alter it with the understanding that a stable pH is better than constantly trying to make it perfect.  Thanks again for your help.  Rich

Answer
Rich,

It sounds like the tank is running fine. Unfortunately, sometimes we just don't know why our fish are dying. All I can say is make sure the water stays clean and the readings stay where they are. If you have this problem again, or any other problem, don't hesitate to ask.