Need some advice - fish dying - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 11-22-2011, 02:40 AM Thread Starter
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Need some advice - fish dying

Hi all,

I have a 20G tank with 2 Corys, 2 angelfish and a pleco. About 3 weeks ago when I was away on a business trip, my kids were brought to a fish farm by their school and came home with a dozen mollies caught at the farm. My wife promptly dumped the mollies into my tank.

The mollies of course started to die. Sometimes one per day, sometimes two. Even more alarmingly, one of my corys died and both my angelfish as well . My tank now has 3 mollies, 1 cory, and 1 pleco.

I don't know what to do now. Is my tank infected with some kind of disease from the farm? Is that what killed my angelfish? Should I siphon out all the water and replace with new water, or maybe siphon out 75%? Do I need to clear out my cartridge filter? I'm completely at a loss.


Unrelated question - The cartridge filter was bought 6 mths ago, my first. I've cleaned it out twice. Every time I try to fix it back it won't pump. I don't recall what I did eventually to get it started but I remember spilling a lot of water onto the floor. It was very painful.

I googled around and apparently I need to "prime" it. How do I do that?
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post #2 of 10 (permalink) Old 11-22-2011, 02:51 AM
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So I'm taking that your tank is cycled.

Yes the mollies that were bought back most likely killed your fish. The probably bought some kind of disease with them, as they may have been exposed to disease at the fish farm. We're there any symptoms? Without any symptoms you can't do much. It could be an ammonia spike as well. Adding so many fish and overloading your bio load. If your not attached to the mollies give them away. If the fish have red gills or other signs of ammonia poisoning they will most likely die, I'm sorry to say. To my understanding ammonia poisoning is uncureable.

Do a 50% water change daily is my only opinion at the moment, due to you don't know what is infecting your tank. But if it is ammonia poisoning the water changes will remove ammonia and you may want to do 75% daily, using a chlorine remover and making sure you don't kill your good bacteria.

Cartridge filter is an external filter? Priming it is simply pull water in through the intake and through the out take. Sometimes the filter has a automatic primer where you can press a button and it will siphon water into the filter. You also do this by sucking on the outtake.

HTH
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post #3 of 10 (permalink) Old 11-22-2011, 02:51 AM
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What are your water parameters? Dumping 12 fish into an already overstocked tank surely gave you an ammonia spike. It is also very possible that the new fish brought disease and/or parasites into the tank. If you could give us a bit more info, starting with your water parameters and any symptoms of illness that the fish may have been showing before they died we may be able to help. But you really haven't given us much info.

I would start by doing a large water change as I suspect poor water quality to be at least part of the problem. But really you need to test your water. Whatever you do, don't change out the filter cartridge as that will make the problem worse.
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post #4 of 10 (permalink) Old 11-22-2011, 02:58 AM Thread Starter
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I don't have any water testing kits so I don't know. But my tank is cycled and was under stocked if anything. Only 2 angels, 2 Corys and a small Pleco.

I'm not particularly attached to the mollies but I want to keep my Pleco and remaining Cory cat. Would the large water changes affect them adversely? I don't have a quarantine tank to keep them in.

If it was some disease, would water changes help?
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post #5 of 10 (permalink) Old 11-22-2011, 03:03 AM
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Doesn't matter if your tank was under stocked. The bacteria only grow to the amount needed ie how many fish there were in the tank when cycling. Adding fish slowly will allow the bacteria to build up slowly.

I can't see large water changes affecting the fish, providing your water is safe ie no chlorine ammonia, nitrites, nitrates and pH.

Depends what type of disease. I can't see it doing harm to your fish.
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post #6 of 10 (permalink) Old 11-22-2011, 03:31 AM Thread Starter
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Ok, here's the plan. I'll give away the mollies and do large water changes daily for a week. Eventually I plan to repopulate the tank. Can I do it in time for Xmas?

How should I go about doing it? If say I plan to get a dozen tetras should I introduce them slowly (e.g. 2 at a time per week) or all 12 at once?
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post #7 of 10 (permalink) Old 11-22-2011, 07:19 AM
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You'll want at least a small school of tetras so I wouldn't do less than 6 at once.

But can you tell us more about your tank? How big, how many fish will you have after the mollies are gone, and what kind of substrate and filter system do you use? And what kind of tetras are you getting? Some are hardier than others (and sizes are different as well)
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post #8 of 10 (permalink) Old 11-22-2011, 07:40 AM
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A 20G, regardless of Long or Tall, is usually not adequate for tetras as most tetra species get to be over 1" and closer to 2" and like to swim back and forth.

I have 6 neons in my 20G half-moon and despite loving them in the tank, I think a longer tank is more appropriate.

I would recommend Harlequin Rasboras or Espei Rasboras. You'll be able to comfortably fit 12 and they'll look great.

Its possible that the mollies introduced an illness or infection that killed off your other fish. The only way to really tell is to monitor them and look for any physical symptoms. Its also possible that the mollies stressed your tank beyond its limits. What a cycled tank really means is that your tank is cycled for the level of ammonia and nitrites introduced into your system - which is mostly based on your stocking levels. So although your tank was ok with your original fish, an addition of 10-20 mollies introduced much more ammonia (through waste and uneaten food) and its possible your tank wasn't cycled for that load. In a heavily planted tank the shock of the load would be mitigated as the plants would be able to absorb much of the ammonia. So it does depend.

In either case, I would only introduce a few new fish (assuming tetras/rasbora size) at a time. Keep a close eye on the ammonia and nitrite levels. If all is good for a couple of days, then you can introduce a few more. 6 at a time should be ok.

Your main focus though should be making sure the tank is safe for new fish - as in infection/illness free.
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post #9 of 10 (permalink) Old 11-22-2011, 06:10 PM
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You need to quarantine any new fish for about a month before adding them to your tank. Once you are sure they are healthy add them a few at a time over a period of a few weeks. Doing both these steps should help ensure that this same problem doesn't happen again. And I would strongly recommend purchasing a drop test kit for ammonia, nitrite, and nitrate - without it you really have no idea what is going on with the chemistry in your tank

And yes, your tank could easily be overstocked as you didn't mention the size of the angels nor the type of pleco you have. Common plecos, even young ones, produce alot of waste and get huge, and adult angels are quite large and will probably outgrow the 20g tank.

Cories are schooling fish and should be kept in groups. I would consider getting more the of same type before adding anything else. Or rehome the one that is remaining.

Last edited by wendyjo; 11-23-2011 at 12:06 AM.
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post #10 of 10 (permalink) Old 11-22-2011, 07:11 PM
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Piling on a little bit, in agreement with what people have said:

I think you have two issues:

1. The mollies probably brought in a disease that's killing fish off.

2. You were over stocked. Angels will ideally have in the range of 15gal per fish. A pleco will out grow your tank. Also, I'd do some research into compatibilities...

Sounds like you need more tanks! :P
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