May I suggest for you to purchase your own test kit (not the strips) check for the three main tests PH,ammonia and nitrites.Tell me me what you have.Also tell a little about your setup size tank,filter,temperature,how much you feed and so on. Are they all male swordtails (they have the long tails)

There were 3 female and 1 male swordtail. At the moment there is 1 female and the plecto left in the tank.

I have been feeding them flakes twice a day. The water temp is upper 70's to 80F. The tank is 20 gallons with artificial plants and rocks. I'll look into the test kits when I go to the store tomorrow.

I stopped at 2 different pet stores today to see if they could offer any suggestions. The first one was an independent mom & pop shop. They said that swordtails can be difficult to keep and are not as hardy as most things you read would have you believe. Their best guess was some sort of parasite that live bearers are prone to. They said that the majority of the fish they quarantine in their hospital tank are swordtails. The second place was the chain pet store where I purchased the fish. They weren't so helpful or knowledgeable. They asked about tank conditions, water temp etc then said "it's really hard to tell" He did say that a 50% water change was too much and that I should never do more than 20% or else I would deplete too much of the beneficial bacteria.

70-80 to wide spread of temperature.50% is too much water to change at one time.25% is ok to change

Hey Lunamoom

Water Change - I do a 50% water change on my tank all the time and i have a very successfull tank for alot of years. The fish are accustom to your water there is no reason i can see where used water which contains the toxins is good to leave in.

Stress - fish are stressed out when transported which lowers their immune system. The white cotton may be ick, the ick have three life cycles: attached to fish which is the growth, detaches and falls to bottom is when it divides and creates a shitload then the case bursts and the ick look for new fish, this stage and only this stage can you kill the ick.

water - i have well water so i have 'clean' water, if you have city water then you have to worry about chlorine. you may want to test your new out of the faucet water to see if it starts out acidic.

fagannutsy
Ick is not like white cotton.What kind of fish do you have? A 50% can stress out fish.City water is usually not acidic

Citiworm,

Ick is like cotton, white spots, how would you describe ick?

why would a 50% change stress fish out. You are removing old water and filling with clean water, the only differ is the toxins. i do it so i can say it does not stress them out. People are told not to so they do not that is why so many people say not to without a reason why.

City water can be anything depending on how it is treated, it can be acidic or basic.

I have community fish mostly bala in a 265 gallon.

fagannutsy
Ick is like grains of salt not cotton.Remember ick is a parisite. This is why people in general treat fish with the wrong meds and end up with killing the fish.
A 50% water stresses out by the difference in the old and new water.Also if when you are changing the water and their is a difference in the temperature that can cause the ick to show.If you do not overfeed,don't have a crowded tank and keep up on your 25% weekly water change there should be no reason to do a 50% water chnge.Just because you do a 50% water change this doesn't mean it does not stress out fish.
If you check the PH of your North New Jersey (I am also from North New Jersey) city water the water PH will be from 7.0-7.8 in most areas(I still haven't found any area under 7.0 which is neutral).

lunamoon
Livebearers are grazers.If you can a fish food with spirulina(algae)in it this with help their immune system. You can feed them 2-3 times a day but not what the fish food containers say what ever they can eat in 3-5 minutes that is too much food. Feed them small amounts.

Citiworm

I had many outbreaks of ick in my time and I would never call it an appearance of a grain of salt, I will call it cotton or white spots, you can call it salt however alot of people will have different descriptions for ick.

I know what signs a stressed out fish wold show and I do not see any when I do a 50%

White spots maybe. Cotton no,cotton describes fungus.

Yea I wonder what causes the many times you had ick in a home tank. A 50% water change with too much difference in temperature maybe the cause. Ick attacks weak stressed out fish first.

Have you checked the PH of your city water?

Citiworm what the hell are you talking about, when i said i have seen ick i was reffering over my 25 year history of having a tank.

I have not seen ick over 12 years, my fish are at 10 inches plus in size and doing well.

I do not have city water i have well water.

I made a post to help Lunamoon i did not ever say i have an issue or problem

Lunamoon how is your tank doing ?

just a quick comment that the filters now a days are great on having parts that create a spot for the bacteria to live, such as a bio wheel or in canisters have ceramic rings which allow the bacteria to form massive colonies.

Hope all is well in your hobbie.

Here is your quote "I had many outbreaks of ick in my time and I would never call it an appearance of a grain of salt" No reason to swear.
I am referring to all your,what you would call suggestions. City water acidic,not saying it can not but PH more between 7.0-7.8. I do check many northern New Jersey city water locations.
I have also been in this hobby 25 plus years, having tanks,breeding,stores,whole selling,importing,transshipping etc.
When I here descriptions of sicknesses wrong.Wrong descriptions mean wrong things will be done to help save the fish.

Also any filter has area to have benificial bacteria.Gravel beds also have benificial bacteria.

The remaining swordtail and pleco are doing fine. Though I'm wary of adding anything else yet.

I have city water and I use water conditioner with each change to counter any chlorine etc. The test strips show the water pH to be neutral. The water temperature is upper 70's to 80 (not 70-80), around 77-80 and when I do water changes I make sure the new water is that temperature going in.

The tank has a bio and mechanical filter, gravel, artificial plants and rocks.

Right now it sounds good. I would wait a little while before I add any more fish.

Did you check ammonia and nitrie?

Thanks but everything is the same as it was before when the fish all died. That's why I don't know what the problem is.....

The ammonia and nitrite tests come back fine. I test everything once a week.

One thing that should have been suggested is pictures. To properly identify the problem pictures would help. Based on what has been said so far, I would bet that you have a fungal infection. I used to be the aquatics manager of a small mom and pop store. Over the years I frequently had problems with swordtails. If they didn't have ich they had a fungal infection. I treated the fungal infections with Pimafix. It worked very well, although, I did still have losses.

IME, Ich is idicated by white spots that appear as a course grains of salt or refined sugar, usually 1mm in diameter or smaller, look in the texts this is accurate, if your growths are larger it is not ich. Fungal infections appeared to be irregularly shaped spherical cottony growths present on or around the mouth or on the finnage and occasionally around lacerations on the fishes body.

I didn't take any pictures of the affected fish but I did look it up online when the first one showed symptoms. It looked like a fungal infection with the cottony growths. I used Pimafix but the fish still died.