Found two dead fish with no fins, please help!

[Tworely]

Hi all, new to fish and the site and really needing some advice. My daughter wanted an aquarium so my sister gave her a used ten gallon tank/heater/filter to start a few months ago, she started with two little cory catfish and two glass catfish. We lost the glass catfish after only a few days and she was distraught. I used test strips and everything was the right color on the card. I didn't have a thermometer at that point and the water seemed cool, so we bought a new heater and thermometer and new filter. I read about cycling, so we didn't add anything else for a few weeks hoping that the cycling and new equipment would solve problem. I looked up easy beginner breeds and from that got her two mollies. Things were great for a few weeks, but a week ago one of the cory catfish died. My son disposed of him before we got home hoping my daughter wouldn't see so I didn't get to see that one. 3 days ago I got her 3 guppies, this morning one of the guppies was dead and had no fins. When I pointed that out, my son said the cory catfish fins had been gone too. So my question is do I likely have a bully, incompatible fish, bad set up, or is there some kind of sickness that can do this? My daughter is so upset and I feel so bad, any advice to keep these fish healthy would be appreciated!

Tank set up, ten gallons, there is a heater, temp seems to stay about 76. We have a Tetra Whisper Internal Power Filter with BioScrubber for Aquariums. There are 3 little fish houses and a few fake plants. We change out probably about 15% of the water each week and use tetra safestart when we change the water. I don't know if it matters but there is a blue light on at night and we turn the light of during the day. They get fed tropical flakes twice a day.

 

[princesleyaa]

Did you do a fish less cycle on your tank before adding the fish? What are your water parameters? Test strips are not very accurate when testing water. It is suggested you get the API Freshwater Master Test Kit.

 

[princesleyaa]

Did it look like it may have been fin rot?

 

[Tworely]

I'm not familiar with fish, but I googled fin rot and I don't think so. The guppy was fine last night, he was swimming and his tail was big and beautiful. When we found him dead this morning he had no tail fin at all. I have ordered the kit you suggested with quick shipping and I'll do that as soon as it comes in.

 

[princesleyaa]

then it sounds like you have a bully and need to pay more attention to figure out the source of the problem. are guppies and catfish the only ones in the tank? genders?

 

[Tworely]

There are two guppies, two mollies, and one catfish. As far as I can tell from google image search, I would guess both mollies are female, one male and one female guppy and I have no idea about the catfish. I've been watching throughout the day as I could between work and the bigger molly is chasing the other fish, so maybe it's her. If that's the case does she need her own aquarium or more hiding places? What's the best way to deal with a bully fish? Thanks for your patience, we are new to this

 

[TMaier]

My money is on the catfish.

 

[guppylvr11]

I would say the catfish but if you catch the moly doing it then you know. You would probably need to rehome or take back. You can't train a fish to be nice. How big is the tank? What is the setup like? Pictures would be great.

 

[Scottishscales]

I've also seen fish eat the fins off of other fish after they're dead. It may not necessarily be a bully just natural fish stuff.

Mollies tend to be gentle and the same with guppies. If your filter is pushing around too much water the current constantly ruffling the fins can cause stress and death on long finned fish if not corrected. Corys from what I've seen leave fish alone unless they're already dead and they see them as food because corys are essentially bottom eaters. But you need a larger group if you're going to keep it. Corys need to be in groups of 6 or more.

Your best course of action is making sure your tank is cycled like others have already suggested. That is more likely the cause. Your water changes are spot on and getting the test kit is great. I wouldn't add anything else until your ammonia and nitrite read zero and you start to see nitrates on the test kit then revisit the stocking.

Good luck!

 

[Tworely]

Thank you all for the great advice. I'm pretty sure I have a mean molly, I put her in a different tank and everyone seems to be doing good now! Also making some other changes based on your advice