Most of our fish died within 1 day --Please help

So after several weeks to cycle our tank, we finally got our fish. We tested our water, had a pH of 7.4, ammonia was 0 ppm, nitrite was 0 ppm, and nitrate was 15 ppm. We brought home 4 brilliant rosboras last night, introducing them as to not induce shock as was recommended by our fish guy. They were fine in the morning, and when I came home at 5:30 I found two of them dead, and by the end of dinner a third one had died too. We had expected an ammonia spike after introducing the fish to the tank, and did another water test to see how bad it was -- the ammonia was 0, the nitrite was .5 ppm, and nitrate was 40 ppm. We did a 20% water change and waiting to test it again. But does anyone have any clue what might have happened to our fish in our tank? How can we prevent it from happening again?

You may want to test for other materials, ex: copper.
please list your current setup and brands of equipment. also, the location of the fish tank.
what foods are were you feeding them?

whats the temp?
what did you use to cycle... scentless ammonia??
and what pro said.. to many vestibules un known

use any soaps or che/\/\icals on the goods?

We have a 16 gallon bow front tank, its one of those sets that comes with heater, filter, a sample food (aqueon tropical flakes). The water temp was 80F, which we reduced a little now.

We used scentless ammonia to cycle the tank.

We haven't used (at least on purpose) any soaps or chemicals.

We noticed some algea... could that be the reason?

algae?, no...its natural to have algae to form within tanks, but there are some that could be harmful. but i dont think you have that strain.
well...could be the flaked food, who knows how long its been just sitting there.

I really dont think its alge.... Only thing i can think of is something is in the water, (cleaning stuff, soap, windex).... Possible still cycling... I personally dont like to use ammonia to cycle my tanks, I always try to get some used filter/sponge from somewhere... cause that is a pretty large jump from 15ppm nitrate to 40ppm in one day...

When you find out more, let us know... you got my brain turning on this one.

If your tests are OK this is what I think it happened:Tank not fully cycled, probably the NITRITE spike killed your fish. Continue with water change and make sure you use dechlorinated water otherwise you kill beneficial bacteria and you will start the nitrogen cycle again(by the way did you make a water change recently and didn't use a dechlorinator?). Monitor ammonia and nitrite. 5 in 1 test strips are crap.
This is my reccomandations assuming that the tests are OK, but I personally doubt that your tests are OK because you had too soon a NITRITE spike.
Oops: what kind of algae do you have? If is green water that means you have plety of ammonia and your tests are good to go to garbage!

also do you notice any little wight spots on the fish kinda sounds like ich or diseases of some sort pic of the fish or carcass might help

Hey everybody. Just wanted to say thanks for all your help. We took some water in to be tested a few days later and levels had dropped. We ended up getting some new fish, and they are doing swimmingly (bad joke, sorr!) so excited to have the tank going, and some happy healthy fish. Felt so bad for those first guys Can't wait to introduce some more fish later on!

Good to hear I'm happy that things worked out for you. So many people have something like this happen and then turn around and sell there tank at the next garage sale. And that's not fair because they dident really get to enjoy a tank. Happy fish keeping.

I bought 7 H. Rasb.'s last year, and now I only have 2. The five died within 2 days because of a fungus that I couldn't see unless I got REALLY close to the fish. I ended up treating with Melafix and the last 2 are fine. It looked like someone had taken a lighter to their pec fins and melted them together.