Fern

Hello guys! I am totally devastated after a horrible discovery in my 10 gallon tank. When I went to feed my baby mollies in the morning, I found all 23 of them dead at the bottom of the tank. It was devastating, and I confess I hadn't cried that much in a while...

My tank is a 10 gallon one, and has been fully cycled for about six months now. It was originally set up to be a hospital tank, but when all my 4 female dalmatian mollies (who live in a 29 gallon tank) decided to have babies at the same time, I scooped all the babies and put them in this 10 gallon in order to be able to care for them better. I also put in it a few platy babies that were born at the same time. I ended up with about 30 mollies and 10 platies. Since they were very small I didn't worry about overcrowding, especially because I am vigilant with constant test readings and weekly water changes (always with gravel vaccuming).

Everything was going fine (with only a few expected deaths) until about a month ago. I went on a week vacation, and when I came back I found 7 dead babies: 6 mollies and 1 platy. I had expected something like this, but all of the rest looked fine and healthy. I did an instant water change, tested the water, and all levels were either ideal or safe. But every day after that I'd find 2 or 3 dead mollie babies in the morning (they were about 4 months old). I did weekly water changes, and for a whole week and a half none died.

Then 5 days ago, I did my usual water change and vaccuming, changed the filter, cleaned the bio sponge in the dirty water bucket (it was quite slimy), and all looked fine as usual. The next morning, much to my horror and sadness, all 23 baby mollies were laying dead on the gravel. What a horrible sight! The weird thing, though, is that all 5 platies were alive and well, swimming around with no visible problem. And now 4 days later, they are still alive and well.

I know that mollies are susceptible to a few things, especially big changes in water quality levels (like pH), but the temperature was constant, the pH level the same safe level (around 100 PPM), nitrites at 0, nitrates at safe level (just under 40), 0 ammonia, and all else under safe levels.

So my question is: does anyone have any idea of what might have happened?? I feel awful and would really like to know what could have caused this so that I won't let it happen again. Any suggestion would be very welcomed.

Thanks for listening...

Lucy

Hi Fern Welcome to Fish Lore

I'm really sorry to hear about the death of your fish. It must be devastating for you.

I've moved your thread to a different part of the forum where I hope it will the attention it deserves.

We have members with a wide range of knowledge so hopefully someone can help you figure out what went wrong.

Good luck.

KyWildFish

First off, Welcome to Fishlore! Hope you get more than just my input.

With a smaller tank like a 10g the biological balance is substantially weaker. Mollies tend to be much more sensitive to water conditions than platys. I have both and have only seen sickness in my Mollies. The problem is probably your over-care for the tank. You shouldn't be changing filters without a backup already cycled and seeded with bacteria. Also, over cleaning and vacuuming can remove all your good bacteria and start a mini cycle. With that many little fish in one tank the toxins probably built up fast. Also, Mollies are debatable on if they are fresh or brackish fish. I put a portion of aquarium salt in my tank and it keeps them disease free for the most part. I have had a couple of fungal infections that were treated easily with more salt.

That being said I am sorry to hear about the mass die off. I have grown attached to my molly babies too, and could imagine the horror of finding them all dead.

Fern

Dear KyWildFish,

Thank you so much for your feedback! I also have had a feeling that the amount of babies in the 10 gallon might have played a crucial role in what happened, that the system probably got off track between cleanings. I did check the water conditions a few hours after I cleaned the tank, but not before. Perhaps something was off before, and with the water change and cleaning, the water conditions changed too quickly, affecting their bodies. I also probably did wait too long to transfer them to the bigger tank and therefore overwhelmed the 10 gallon. That coupled with too often cleanings didn't help either. A hard lesson learned...

I have a question for you: you mentioned that "(...) You shouldn't be changing filters without a backup already cycled and seeded with bacteria." What I changed (and do so every 2 or 3 weeks) is the replacement filter cartridge with the carbon inside it. I have never changed the bio sponge where the bacteria is collected, I only wash it occasionally in the bucket with dirty tank water to take the gooey stuff off. Is that the best thing, or should I not be changing the filter cartridges so often? Once I kept the filter cartridge for more than 3 weeks in my 29 gallon, and the filter stopped spewing water because the cartridge was so dirty (an overfeeding lesson I learned!). Should I be burying some extra cartridges in the gravel to collect the bacteria and then replace the dirty ones with these? I would really appreciate your opinion!

But one good thing did come out of this horrible mass death experience. It gave me an important opportunity to discuss with my young son the issues of life and death, of the importance and love of pets and what they can teach us, even in death. So bless my little baby fish hearts, their deaths were not in vain...

Thanks!

KyWildFish

The filter should not be changed very often. Most people will only rinse it in tank water and use it till it wont rinse or falls apart. The sponge sounds like it is there to trap bigger particles and probably doesnt harbor as many good bacteria as your actual filter. The box and the pet stores will tell you to change the filter more often so they can sell more of them. If you have enough room put a new filter behind the old one and let it become seeded with bacteria.

Also, your weekly cleaning routine should only be a 20% water change, more if the nitrates are higher than 20ppm. About once a month I bang the filter out in tank water and do a quick vacuum of the substrate. If I have to change a filter I dont touch the substrate.

If you have any more questions I would be glad to field them, but you will probably find better advise search the forum.

Shawnie

if you run carbon though, it should be changed out every 3 weeks as it spirts the nasties back in the tank..so you are right changing that out and just leaving the sponge media rinsed in tank water occasionally

Shadow Sichlid

Sorry about your loss. and sorry i couldn't get to you sooner like they all said with mollies (especially baby's) you cant do too much water changes and (if your using some) keep the chemicals that you put in the tank on the downlow meaning (only if you really need it)

Matt

Sorry To Hear That.

It is part of nature though. Sadly.

From Matt