freshwater problems

[darkreef]

I have a 55 gallon tank.
ammonia , nitrate ect all normal.
but everything i put in there dies.

so lets tell you more about my set up
this is mainly a experiment for me

first time using sand substrate, 6 plants swords, anabis , java fern
i also have slate rock from B.C, if you ever go for a drive to golden bc there is beautiful black slate on your left hand side. i picked some scrubbed it down but it in.

i do weekly water changes of 10% every friday ( with conditioner)
i have a ehiem 186 filter
air pump , heater , and basic lighting

the only fish that is doing great is my red tail black shark (hes not a bully)

what iv lost
first i started off with two chiclids and they just died with in two days
they were babies so i wasn't surprised

two cray fish - one was shy and just died. the other lasted threw two molts and i found him dead today . he had orange on his soft skin . he was super healthy and active

now im stuck with two red tail black fish but i can tell one is on his way out
hes grey , no color , not eating , i can see his heart beat threw his gills .

i got them both at the same time and one has doubled almost tripled his size , i call its a she because shes chunky , black and bright red tail. active and lovely . like i said before they dont bother with each other accept i see them dance every once in a while on a plant but the other is getting to weak


what i feed ( top fin waffers , cobalt (colorflakes)


my questions
* what am i doing wrong?
* is calgary tap water safe as long as its conditioned ?
* my slate has some orange kinda resembles rust stains (will not scrub off)
is that ok?


i can add pictures if you want . i know its alot i wrote but i just wanted to be very clear. this is my first planted aquarium and my first over 30 gallon aquarium .

im trying to get this down so someday i can own a 180+ with a fire eel