Lost 2 fish for no apparent reason

[OhNeil1969]

I woke up this morning to both good and bad news in my 29 gallon tank. Sometime during the past day, my dalmation molly had her fry. Ironically, I didn't know she was pregnant so she wasn't quarantined. There are several molly fry alive and hiding. Also, none of them seem to be stressed and the other tank mates seem to be leaving them alone.

The bad news is that my swordtail and 1 of my zebra danios were found dead. There was no sign of disease or stress prior to this and the water is good. In fact, I checked afterwards and found that I had 0 ammonia, 0 nitrItes and 5 ppm nitrAtes. Both fish looked like they had been attacked but I've had this tank with the same tank mates for 5 months now without any real incident. I've read about other species of fish becoming aggressive when pregnant or after birthing fry but I've never heard of that type of behavior from mollies.

Does anyone have any info about aggression from fish that have normally been passive. I'm concerned that this may just be the beginning.

Currently I have:
4 zebra danios;
5 neon tetras;
9 mollies (2 new born confirmed, 2 about 1 month old);
1 red wag platy;
1 serpae tetra;
2 guppies;
1 siamese algae eater
and 3 mystery snails.

I know it may sound like a lot. The tank, however, is fully cycled. I'm running 2 HOB filters (a TopFin Power 30 and a Marineland Penguin 200 with bio-wheel). I'm performing 2 PWC's per week. There are both live and artificial plants. The live plants aid in filtration and all plants provide good hiding spots. Furthermore, I test the water regularly with the API master test kit. Up until this point I haven't had a real water quality issue. I did increase the frequency of my PWC's due to high nitrAtes a couple of weeks ago. The crappy test strips I was using indicated that all was well when it actually wasn't. So as I said, I really don't know why these fish died. Any info you can give will be greatly appreciated. Like I said, I don't want something like this to happen again.

 

[BigJim]

You're right about that being a heavy stock list. I wouldn't replace the fish you lost.

When did you last do a PWC? Your nitrates are surprisingly low. If you didn't match your water temperature pretty closely, you may have shocked your fish a little. I suppose it's possible that the SAE has started bullying the other fish. A big male molly can also be aggressive.

 

[OhNeil1969]

The last water change was performed this past Sunday. Was planning on doing another change today but held off due to the low nitrate reading. Prior to today I was doing 2 50% water changes a week. I was worried about matching the water temp also. The tank did drop from 80 to 76 degrees after the water change. But none of the dead fish exhibited any change in behavior after the change. As for the molly and SAE; both are about 2 inches and I have never witnessed aggressive behavior from either (one male molly was aggressive to another male until I added the females). Are any of the species of fish I have territorial? They appear to have plenty of swimming room and occupy all parts of the tank. I wasn't planning on adding anymore fish. In fact, as the mollies continue to breed, I was planning on moving them to my 60 gallon tank as soon as it finishes cycling.

 

[OhNeil1969]

BTW, the 5 ppm nitrAte reading may have been 10 ppm. The colors on the API master card are hard for me to decipher between 5 and 10 ppm.

 

[BigJim]

Male swordtails can be a bit territorial, especially toward other live bearers. SAEs can also get aggressive.

In order to drop the tank temperature 4 degrees with a 50% PWC, you'd have to add water that was at least 8 degrees cooler. That might be enough to finish off a weak fish.

 

[OhNeil1969]

Male swordtails can be a bit territorial, especially toward other live bearers. SAEs can also get aggressive.

In order to drop the tank temperature 4 degrees with a 50% PWC, you'd have to add water that was at least 8 degrees cooler. That might be enough to finish off a weak fish.

Would they die so long after the shock? Like I said, there was no change in behavior for at least 3 days after the pwc. I recently read another thread where the poster used a thermometer at the end of the gravel vac to ensure the temp was ok. I'm going to start measuring the temp of the water from now on.

 

[McLumpy]

I'm so sorry for your loss, Neil.

 

[OhNeil1969]

I'm so sorry for your loss, Neil.

Thanks! Like I said though, it was a day of mixed blessings. I'm excited that there are some new mollies. It makes me feel good when I see my fish reproduce!

 

[McLumpy]

Thanks! Like I said though, it was a day of mixed blessings. I'm excited that there are some new mollies. It makes me feel good when I see my fish reproduce!

Oh yeah, I did read that... congrats on your babies!

You're not alone btw, my Gold Dust Molly is due to drop any day now! There must be something in the water because I've seen a lot of prego Molly posts lately. lol