Otherwise, there is the very real possibility that it will happen again. :(

You offer a poll and then offer no options. This suggests a little bit as to where you are at. You seem unclear about what really happened and what you should do. Let's try and diagnose what is happening to your fish (what the toxins are...) and how to you can prevent those disasters from happening again. :)

For starters, would you please look over the 40 questions asked in "20 Questions for new fish owners or owners of sick fish." Yep, the way those grew to 40 is also a little lesson in inflation ;)

http://www.guppylog.com/story/2005/6/24/82111/0134

Especially of importance is that we need to understand where your aquarium is at in terms of the nitrogen cycle and what you are doing in terms of occasional partial water changes. I'm certainly not trying to show off - faithfully keeping up with partial water changes is the hardest thing for me in this hobby too.

If you are unfamiliar with what we mean by the nitrogen cycle, please click on the Immediate Help link at the top, right of this page and skim through the section on "New Tank/Cycling/Setting Up/Water Changing". This is terrifically important for anyone if they are going to be a successful aquarist. One of my mentors in the hobby suggested that (for the group of fish he specialized in) if one could do a PARTIAL (30-45%) WATER CHANGE EVERY WEEK (Freudian slip that the caps came on there) with seasoned, treated water of the same temperature as the aquarium, that over 90% plus of all diseases could be avoided.

When your last disaster hit, you probably had to entirely tear down and rinse out the tank and everything in it. Well done if you did. But that means that the whole process of cycling the tank, often a 4-6 week process, had to start almost all over again. If one introduces new fish before that, it may be a death sentence for them. :(

One of the other things to consider is the idea of a quarantine of any new purchases. That is really resented be newer aquarists. After two wipe outs owing to epidemics brought in or triggered by new fish, the cost of setting up a quarantine tank (often an cheap 10-gallon placed on the bottom of an over-under tank stand) and including a submersible heater, box filter, a little gravel, plastic plants makes financial sense.

Also, and the shops sometimes over look this, new aquarists really need to get a test kit that will check for ammonia, nitrites and nitrates in the water. Probably a kit testing for all three is less expensive than buying individual test kits. Trying to set up one's first tank, especially with today's water supplies, and not using test kits, might be a little like trying to fly an airplane through fog over the Himalaya Mountains without instruments. ;)

Australian physician Bruce Hansen rather revolutionized my attitude towards quarantining new fish when he noted that the quarantine tank is for the benefit of the fish in the regular aquarium. It is so if the new fish are diseased and die, they will not take everybody out in the established aquarium. Sometimes too the stress brought about by new aquisitions (especially fish that don't get along with the old residents and cause a lot of stress) will trigger an epidemic among those fish always there. Many organisms that can negatively effect our fish are already in the aquariums and even in out public water supplies - at a hopefully non-lethal concentration. (Sort of like how we encounter viruses, germs, molds and other wee beasties all over the place in the course of a day. If we are healthy and our immune systems are up to speed, the pathogens don't bother us.)

If the new fish get sick and can be successfully treated, wonderful. But the odds of effectively treating diseases like columnaris (for instance) are very slim. Better to lose the new purchase than lots of old friends.

We also have to watch that we do not crowd our tanks like many shop tanks are crowded. They are probably doing daily partial water changes. (And if not, they are probably removing a lot of bodies before the store opens.)

This sounds really nasty in human affairs, but in the past many countries quarantined immigrants. Whole ship loads (in the 19th century) of people died. But the host country felt that however tragic that was, it was better to lose people on a ship, than tens of thousands of residents in their city.

The cost of test kits is often resented, I realize. But that is cheaper than leaving the whole darn aquarium set-up out by the curb on garbage day.

The testing for those toxins in the water sounds frighteningly like chemistry. However we routinely take showers and shampoo one's hair, cook meals, fill our cars (when we can afford it) with the correct blend of gasoline and even succeed at growing gardens or at least something passable as a lawn. If we called all that hygienic chemistry, kitchen chemistry, automotive chemistry and horticultural chemistry, we'd probably panic and die of neglect. ;)

Please consider that list of questions alluded to at the beginning of these comments. Answer what you can, when you can. (I'm typing this out in a word processing program off-line, saving the text as I go, because otherwise I too often time out on forums and even lose everything plunked out. You are probably more experienced at this than I am and already are very familiar with this strategy.)