Fish dead in less than a day?

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Bet the fish where sick when you got them... walk into almost any lfs ( even the best mom and pop shops) and mollys/livebearers are often sickly... at least one or two I can always pick out if not more ( chain stores usually 1/2 of them have fungus) Spend time watching the fish before you purchase them.. and don't be afraid to pick out the healthiest ones and have them get you those... it's your fish, your money , ect... I use to go out of my way to show new tank owners the difference between healthy and sick fish when helping them... it can make a huge difference.

50% wc and you should be fine to get new fish in a few days... make sure the gravel you have isn't coated.. salt can cause erosion... if the bag says not for saltwater use chances are adding salt can cause a toxic reaction w/ coated gravel. but 2 mollys in a 20gal shouldn't be dead in 24 hours.
 
how exactly did you cycle it? did you add ammonia? live cycle? It does take longer than three days to cycle a tank, but i don't think that's what killed the fish. I think you just bought sick fish.
 
My guess is they died from not being acclimated correctly since they dropped so quick, the cycling process would have probably go them a few days after.
 
I used API Aquarium Salt for Freshwater Fish.

http://www.petco.com/product/1697/API-Aquarium-Salt.aspx

But the black one seemed dead before I put that in.

To acclimate them, I let the bag float in the tank for 20 minutes... then put some of my aquarium water in the bag for another 20 minutes or so.... then just let them in the tank.

I didn't do anything special to cycle it. Just let it run with the tap water conditioner for a few days, as it said in the instructions.
 
must be sick fishes, ive done worse than that too many times when i was young, not a cycling problem
 
So I just tried to get started with my first fish tank. Bought a 20 gallon Aqueon kit. Washed my gravel / decor and put it in with water and water conditioner. Tossed in a filter and turned on the heater... then let it cycle for three days. After that I went and picked up some fish from the pet store.

After less than 24 hours the fish didn't seem right. One was always at the top of the tank and his fins were all clamped down. The other was just laying on the gravel the whole time.

I ran to the pet store to get advise. Picked up a Nitrate and Ammonia test kit and some salt so I could make the water brackish.

Nitrate and Ammonia tests showed practically zero. I added the salt, but I'm pretty sure one fish is dead already.

The fish were a Black Molly and a Dalmatian Molly.

Black Molly is just laying on the gravel, seems dead, doesn't even seem to be breathing.
Dalmatian Molly is laying on the gravel barely breathing.

What did I do wrong?

Temperature seems steady at 78'ish according to two different thermometers. Can't think of what I did wrong.

Want to fix my problem before I buy new fish. Pretty sad for these ones. Maybe the Dalmatian will pull through... but I doubt it.

You didn't cycle long enough or use the right method.

A proper cycle requires 3-4 weeks of cycling and you need to have a source of ammonia to build up the bacteria with (fish poop if using fish to cycle or some for of rotting material like a market shrimp or some fish food left to rot at the bottom).

I recommend a fishless cycle because it is more humane and allow you to reach a full stock sooner than a fish cycle. A fish cycle requires you to very slowly add one small fish at a time over the course of several months and the fish have to be very hardy, which usually means they are fish you don't really want anyways. Plus a fish cycle requires frequent water changes, which inhibit bacteria growth.

A fishless cycle has you drop some food (a market fresh shrimp from your local grocery store or decent amount of sinking fish food pellets/wafers) and let them rot. The ammonia will spike, causing bacteria to grow and consume the ammonia to release nitrites. Ammonia will drop to almost zero and the nitrites will spike and more bacteria will grow to consume it. The nitrites will decline to almost zero and the nitrates will spike. Once the nitrates drop down to low concentrations, the tank is ready for stock. At this point, the tank should have taken about 3-4 weeks to cycle. You can speed this up by adding some of the bottled bacteria they sell once every day. This will make that initial 3-4 week cycle down to about 2 weeks. It is recommended you do 1/4 the tanks full stock and let them settle in for a week after the initial cycle is done. The bio filtration (bacteria) will grow to accommodate them. At the end of the week, add another 1/4 stock and so on for the next couple of weeks until the tank is fully stocked.

A fishless cycle will have your tank fully stocked in 2 months while a fish cycle can take 3-4 months and often results in dead or seriously stressed fish.


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I also think that you probably bought sick fish. There is practically no way that they were suffering from ammonia or nitrite poisoning so early on.
 
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