I bought 3 plecos and 3 zebra danios and within 4 days 2 plecos and 1 danio were dead?

Question

I set every thing up right but i fear for the other three so whats going on

Answer 1

what size is the tank? is it cycled? sounds like you added too many fish to the tank too quickly

Answer 2

Too many fish too soon.  Is your tank cycled?  I certainly hope so, otherwise you shouldn't have ANY fish in there or the ammonia build up will kill them all.  If you didn't cycle the tank first then it wasn't set up correctly.

Even if the tank was cycled you need to add new fish slowly to allow the bioload to adjust properly.  How many gallons is your tank and what kinds of plecos were you putting in there?  3 is a little overkill for plecos and some species get up to 24 inches which you would want to avoid that kind unless your tank is 100's of gallons.

Without knowing whether you cycled or not or how many gallons the tank is it will be hard to help you.  You should go to any popular fish site if you haven't or don't know about the aquarium nitrogen cycling process and complete this fish.

If you have done this test your water with a liquid drop test kit for ammonia, nitrites and nitrates.  The first two should be a flat 0 and the last less than 20 ppm.  If this is off it can stress fish out and kill them.  Ammonia is toxic in any amount and nitrite is still about 50% as toxic.

Good luck: )