posted 02-12-2004 08:50 AM         

What size tank?
What type of filter?
How many goldfish?
What size are the goldfish?
What are your water parameters (ammonia, nitrIte, nitrAte)?
How often and how large are your water changes?
When you said you tried changing the filter, did you replace all the media at once?
What symptoms are they showing before they die?
What chemicals have you tried?
Are you using dechlorinator?

posted 02-14-2004 09:58 PM         

I just bought a new gfish and he's a koi and he died in like a week. Is there like any way to prevent shock because thats what the dude at the store told me....

thanks

posted 02-14-2004 10:52 PM         

First of all 10 gallons is way too small for 2 goldfish (it's really too small even for 1 goldfish) and it's definitely too small for a koi.

4 - 5 months is WAY too long to go w/o doing a water change even if your tank was big enough. Through a process called the nitrogen cycle bacteria in your filter convert ammonia (which is toxic)produced by fish into nitrIte (also toxic) then into nitrAte. At levels below 20ppm, nitrAte is not toxic, but long term exposure to levels above 20ppm will kill your fish. And the only way to remove nitrAte from a tank is to either have TONS of plants or do water changes. Normally, for messy fish like goldfish and cichlids, WEEKLY 25% water changes are needed to keep the nitrAtes to safe levels. By 4 - 5 months, the nitrAtes levels were so high, your fish were being poisoned to death. One other thing to note is the less water you have, the less the nitrAte is dilluted, so the quicker it builds up.

When you replaced the filter, if you just removed the old one and put the new one on, you just threw out all the bacteria I mentioned previously so not only were there hight levels of nitrAtes, there were no bacteria to convert the ammonia so those levels were probably really high too and that's another thing poisoning your fish.

So, my suggestion is if the 2 remaining goldfish are koi return them now because they aren't suited for anything other than fairly large ponds. If they're one of the fancy varieties of goldfish, you will probably need AT LEAST a 40 gallon tank ASAP. For the time being, do a very large water change to at least get your water parameters closer to a safe level. I recommend 75% but if you do do one that large, it is very important that you make sure the temp of the new water is very close to the temp of the old water.

You should also buy test kits for ammonia, nitrIte, and nitrAte. These will help you make sure your water levels are safe for the fish and give you a better idea of how often you should be doing water changes.

I also suspect your tank isn't cycled any more (because you changed the filter). Normally, I don't like recommending it because I've never actually used it, but I think you should look for a product called Biospira. It contains the beneficial bacteria I mentioned previously, and if used correctly, should instantly cycle your tank. But like I said, I've never actually used it so I don't like recommending it, but at this point, I don't think it will hurt to try it. One note, though is you should avoid any similar product (like Stress Zyme or Cycle) that isn't refrigerated because by the time you get it, the bacteria will be dead and worthless.

And if (hopefully it's "when") you get a larger tank, you will need to cycle it before adding the fish. Here is a really good article that explains in more detail the nitrogen cycle, why, and how to do a fishless cycle.