What to do? tropical fish tank of doom

Question

we set a 30l tropical fish tank up in June this year, after cycling it for 3 weeks we put in 5 guppies which died one by one over next two weeks.

Last weekend we put in 4 cardinal tetras and 3 zebra danios, after some tetras died we put in 3 neon tetra to keep the shoal size up.

today we have 1 danio left, two cardinals and 3 neons (sorry this is sounding like a maths puzzle)

water temp has been around 25/26 c

ph 7.2

nitrates 10ppm

nitrites &ammonia less than .25ppm

we addded the fish as per the instructions from the shop,

there have been no visible signs of disease in the neons and danios, they just get sick and die within a few hours.

what are we doing wrong? how can we stop all the fish from dying? (and for those who like maths puzzles how many fish have died :P )

help us!

Answer 1

you havent mentioned if you have put safe water in which controls the chlorine in your tank (very Important)

also do you have any wood in the water if so remove it,wood should only be added to a seasoned tank,

also you can get some crystals which set your ph level a good one is ph 6.5 which is suited to most fish,

another thing you can do is take a sample along to your local pet smart shop or large pet superstore and ask them to test your water for you which is normally free of charge,they will then advise you on what fish are suitable for your tank, but be carefull not to buy your fish from there,by all means buy your chemicals and accessories but dont buy the fish from these stores as they dont look after their fish but are good for advice.

also what filter do you have as you must have a good one and my advice would be to take your charcoal out of the filter,when i started my tank up i had a similar problem as yours and my local shop told me to take the charcoal out and since then i had no problems.

it acts as a filter of the water so when you put in treatments the charcoal soaks up all the treatment and your fish never benefit.

in my tank i have four albino cat fish which clean the bottom of the tank,two coolie loach which you never see as they live in the gravel and clean it,a pleck which cleans the glass and two clown loaches and then my normal fish,

it is a good balance to have and has stood me well for the past 4 years,

once you get the balance right you wont need to do much with your tank,

my advice is to start off small and build up every 14 days,

Dont change your water too often

Answer 2

You are probably overfeeding the fish.

Personally, i never had a good luck with cardinals, so be happy that two are left :p

Your pH should be less to have thriving tetras(they like it acidic) but i don't think that the pH killed them.

I recall having fish dying in a 25L tank. Guess what was the problem???? A too powerful filter!!

i hope that the info helps you.

Answer 3

10 Fish Have Died

Answer 4

i think the ammonia should be at 0

Answer 5

Sorry but your tank may be going through a mini-cycle through adding too many fish at once.  Danios are quite a hardy fish for cycling tanks but not with those numbers.  Please be patient, trust me I have gone through the same thing after many years break from tropical fishkeeping and am playing the waiting game to add more to my 40g tank.

Answer 6

Neons and Danios aren't the best fish to start with, they tend to be picky about living conditions.  Try a few sturdy Mollys, platys or guppies.  

Where are you getting the fish?  Petco, Petsmart, and Walmart don't take good care of their fish. They may have been sick/dying before you got them.

What is the weather like outside?  If they get too hot or cold on the drive home, they can die.

The fish come in bags from the pet store.  Float the bags in the aquarium water for at least 20 minutes before you put the fish in the tank.

Did you rinse off everything before you put it into your tank?  Sometimes bacteria and other contaminants hang around.  That includes filters, tubes, decorations, etc.

Decorations can "leak" toxins into the water.  Avoid metal, and any un-water proof paint that may come off and cause contamination.

What to try?

Live plants.  If you don't already have them, give them a try.  They condition the water, and are covered in beneficial bacteria and other "critters" that may help.

Products like "Stress Coat" and "Stress-zyme".  They'll help the fish make the transition to your tank and help bacteria growth.

Specialty aquarium stores offer the best fish and expert advise.  It's worth the extra money to have healthier fish and knowledgable people to help you.

EDIT TO ADD:

If it was me, I'd leave the surviving Danio on his own for now and get 10 feeder guppies.  They're nearly indestructable and may (probably will) "straighten out" the problems with the tank.  

If they survive a month, try Danios.  Replace them (guppies) as they die off.  (Which is why I recommended feeder guppies.  They're cheaper than Mollys and Platies)  

Another tip is to let 1-2 dead guppies stay in the tank.  Decomposition is usually a bad thing in an aquarium, but sometimes the beneficial bacteria need a really good meal to get "jump started".  

I just had another thought.

You don't mention feeding schedules.

You should be feeding 1  meal a day.  Fish stomachs are about the size of their eye.  Use that for portion sizes.

Fish can and do eat themselves to death.

Answer 7

are there any other signs of sickness. white spots, floating, sinking, wobbling? do you fully change the water after the fish die off? if not that could be your problem reoccurring. try to get the ammonia level as close to zero as possible. otherwise i suggest you start over (that may sound a little cruel but if your problem keeps going on in this cycle you will keep having dead fish.obviously) so if your fish die clean you tank from top to bottom with completely new water and clean filter.

maybe ask your closest pet shop person, they will know more about what you can use to treat it