Why does after each water change one guppy die?

Question

I have a medium-size aquarium and there are about 24 guppies in there (I got my guppies about 6 weeks ago). Every time I do a partial water change (I take about one quarter of the water out and put fresh water in) one guppy dies, usually within two days. In the last 5 weeks 5 guppies have died. I do water changes once a week. Whenever I do a water change, I mix Tetra Aqua Safe and Aqua Balance into the fresh water because I heard that this is necessary to make the water safe. I mix about half a spoonful of each in the fresh water. I wonder what I'm doing wrong.

Answer 1

You know.. guppies are very hardy..  i cycled my 30-gallon tank with 14, and none of them died.

#1, Is your tank cycled? If that.. that could be a reason.

#2. I'm not sure what those products you put are, but all you need, is de-chlorinator. And add to the new water for a minute BEFORE pouring it in the tank. If you don't do that, the chlorine in your water might kill your beneficial bacteria, and you have to re-cycle your tank again.

#3. Mid-size tank. So it's about 20-30 gallon?

That's where too small for 24 guppies. Maybe it'll keep dying till you have the right number. Remember, it's 1-inch of fish per gallon MAX. A guppy in adult form is about 1.5" - 2". So do your math.

#4 Disease? Maybe some of your guppies are infected? and are spreading it out to others? Check for signs of disease, and research on the net to identify the problem, if there is any.

Hope this helps

Answer 2

How big is your tank?  If you have more inches of fish than gallons of water, your guppies might be dying because the biological filter is overloaded.  Was your tank cycled before you added the guppies originally?  Meaning, did you see an ammonia spike, nitrite spike, and the subsequent presence of nitrates?  If your tank wasn't cycled with fish for at least 4 weeks before you added the guppies, this could be to blame.  There's also the possibility that the tank was cycled, but you added the 24 guppies all at the same time and caused your tank to start a mini cycle.  

If none of the above fit the bill, maybe the water you are adding into the tank during the partial is somehow drastically different than the water you have taken out.  I'm not familiar with the chemicals you are using, but as long as you are dechlorinating the water, matching the new water's pH to the tank water's pH, and equalizing the temperature, everything should be fine.  New water, even if it's dechlorinated, can cause stress if the pH and temperature do not match that of the water taken out.

EDIT

As per your additional details, it appears your guppies are dying because they are being kept in an uncycled tank that is too small for such a large group.  You can only keep 5 inches of fish in a 5 gallon aquarium.  You can figure out how many gallons your aquarium is by multiplying the dimensions of the aquarium in inches (length, width, height) and dividing that by 231.  It would probably be a good idea to return most of the guppies (keep about 2) to your friend and cycle the tank before adding more back in.