Help! Fish dying!

[boomalatty]

Hi,

We recently started a 20 gallon tank. We did a fishless cycle, then did a large water change. We stocked our tank about 2 weeks ago after getting some advice on here (many thanks) with 6 neons, 2 guppies, 1 platy, 1 clown pleco, and 1 dalmation molly. We used Prime conditioner. We have checked our chemical levels every day with an API Freshwater Master Test, and our ammonium and nitrites have stayed at zero. We've tried to do everything just as we've learned on the forum. Everything has mostly been fine for a couple of weeks, except that the molly seemed to be very territorial and nip at the other fish. Initially, one of the guppies died not long after stocking. He seemed to be picked on the most by the molly. Then, within the last couple of days, all the fish suddenly died, except the molly. I'm not sure if it could be some type of disease, or whether the molly has been so much of a bully as to stress or injury the other fish to cause these deaths. If it's a disease, I imagine she would soon go too. We didn't see anything visibly wrong to indicate disease though.

Any help would be appreciated as we try to resolve this issue and successfully restock our tank.

 

[Byron3991]

Have you been doing water changes each week and what are your nitrate levels at? It took me a lot of water changes to get my nitrates down after I cycled my tank. Also, any visible signs of trauma on the other fish besides the first guppy?

 

[Mumma.of.two]

How are the fish acting before they die? Any marks? Fuzz? Spinning? Gasping?

 

[DJNut]

I had a Molly that bullied my other fish, it is because they need more Mollys with them, I put a male and two female with her and she was fine, left my other fish alone.
Dave

 

[Coursair]

Hi,

We recently started a 20 gallon tank. We did a fishless cycle, then did a large water change. We stocked our tank about 2 weeks ago after getting some advice on here (many thanks) with 6 neons, 2 guppies, 1 platy, 1 clown pleco, and 1 dalmation molly. We used Prime conditioner. We have checked our chemical levels every day with an API Freshwater Master Test, and our ammonium and nitrites have stayed at zero. We've tried to do everything just as we've learned on the forum. Everything has mostly been fine for a couple of weeks, except that the molly seemed to be very territorial and nip at the other fish. Initially, one of the guppies died not long after stocking. He seemed to be picked on the most by the molly. Then, within the last couple of days, all the fish suddenly died, except the molly. I'm not sure if it could be some type of disease, or whether the molly has been so much of a bully as to stress or injury the other fish to cause these deaths. If it's a disease, I imagine she would soon go too. We didn't see anything visibly wrong to indicate disease though.

Any help would be appreciated as we try to resolve this issue and successfully restock our tank.

Mollies vary in their personality. I see many that are bullies and what I would call semi aggressive.
More Mollies may help, but I like a peaceful tank.
Mollies breed too fast. Two males may fight. I'd return the Molly and give your small fish a break.

 

[boomalatty]

Before we added fish we did several large water changes to get the nitrates down to zero. We've continued to with weekly 10-20% water changes, so they've remained very low.

As for the fish, we're haven't noticed fuzz or anything like that. They seem to look fairly good until the very end, when they more subdued and tend to find a place to hide before passing.

Aside from the molly, which seems to be going strong, I don't know what else it could be. We have a pretty "normal" tank (gravel, plastic plants, real driftwood, fake coral cave).

I think I'm going to try to convince my daughter to return the molly. She really likes it though and asked whether the molly might be more compatible with other types of fish, maybe even semi-aggressive. Any thoughts?

Thanks for your help.