Hi Bartok,
I feel for you. Nothing sucks like losing fish the way you are.
Hang in there. It's a fine hobby, you just have to get everything going.
If I may humbly submit my advice:
First, this should go without saying, but no more new fish until the deaths and sickness stop, or the tank is empty. You have to get a handle on what's going on, or the tank has to come to an equilibrium point to deal with it. Either way, no more new fish for now.
Second, get a nitrate test kit. It's an invenstment you should make for the long-term if you're committed to keeping fish anyway. You need as complete a picture of your water chemistry as possible. There's definitely something wrong, and it might very well not be nitrate, but a simple test will tell you. When you have problems of this scale, you can't assume anything.
Third, I think you may have had stocking problems, both in overstocking and in combinations of fish. No way can a betta thrive in a tank with tiger barbs long-term.
Again, for the moment leave what you have in the tank in there, and once we're sure the problem (whatever it may be) has gone away, then look carefully at where you are stocking-wise and determine what it might be safe to add (if anything). It might not seem that small, but 16 gallons is not a large tank, and that works against you when something is out of whack.
Also, fish don't generally starve to death, although it can happen. It takes a healthy fish quite some time to do so. I'd be willing to bet your fish that quit eating did so because he was sick from whatever killed him. I don't think it was starvation that did him in. Fish that won't eat are almost always unwell. It's typically an indication that something's wrong.
Have you added any medication or treatment to the water other than the Coppersafe (which I'm not familiar with)? Melafix is a good general tonic-type treatment for sick fish which is usually quite safe. I might recommend using some of that in your tank, but it's not always wise to mix medications, so I don't know. Given your current state though, I don't know if it could hurt.
What specific product are you using to dechlorinate your tap water?
Hang in there. The tough times don't last forever, but it really sucks when you're going through one.
pendragon!
)
