Hi Robyn

I bought the guppies the middle of Jan. I got 4 males and 3 females.I also put in 4 Neons at the same time.They are in a 20 gal tank with my two small plecos. Everything was great for a short time.I even had baby guppies and was able to save about 20 of them and put them in a small tank.They are coming along fine.
One by one I am losing the guppies.I was going back to the store and replacing them but gave up on that.I thought maybe I just had to many fish in the tank.I did a water change and treated the water.I have done everything I can think of. Yesterday I was down to 2 females and one male.The male was attacking the one female all day.He was wouldn't stop biteing at her and chaseing her.Today she is dead and he has started picking on the other female the same way.I do think that both female were going to have babies.Is it possible that I have a killer guppy or is there something wrong with the tank? I was also thinking I might have a parasite in the tank by the way some of the fish are acting.How do I know for sure and how do I get rid of it ? Will it have any affect on the Neons and Plecos?
Please help me save them.

swampview

I'm sorry to hear about your guppies. Sometimes a guppy may be more aggressive than another but they usually aren't killers. If the females were weak or sick, then the male may have picked on them because of that (in addition to wanting to mate). You may never know why they died. I usually don't know for sure why a fish of mine has died. Neons are usually less hardy than guppies. Plecos can be pretty strong and resist parasites (and other problems). What is the pH and hardness of your water? Guppies like it sort of hard and a pH of about 8 whereas tetras like it below a pH of 7 and soft water. If your water is soft and lower in pH, then that would make it harder for the guppies to live. Did you add salt to the water? Guppies do better with some salt. A tablespoon per 5 gallons works for most fish. If you're worried about parasites, you can try a general parasitic medication. Keep in mind though that the medicine could harm the remaining fish, and if the fish do have a parasite, there's no guarantee that the medication you use would actually kill it. I assume you've been testing your ammonia and nitrite levels, and they were okay?

If you try more guppies in the future, be sure there are lots of hiding places and more females than males. I don't keep guppies because my water is soft although I had them when I first started with fish. I had a few that produced a few dozen babies. They were doing fine when they all came down with something (I can't remember exactly) so I added some antibiotic. Unfortunately, I chose penicillin which killed all the good bacteria. All the fish in the tank (which was overcrowded) died when the ammonia spiked, except for Plecy (who is now 15" long and 12-years-old).

Hi Robyn

Thanks for the information.I don't have the equipment to test the ph in the tank.I know the water here is soft well water.No I have never add any salt to the water.I think next time I go to the store I will buy what I need to test the water.Funny you should say the Neons are harder than the guppies because I'm not having any problems with them at all.I think I will just wait and see how the last female and male do.I have about 20 baby guppies and maybe I will just raise them.

Thanks swampview

It sounds like you have soft water that's probably a pH of 7 or less. The neon tetras like that; the guppies don't. That would explain part of the situation.