Something is wrong with my tank-

35% Off ! All WYSIWYG fish and corals
So I have a Mr. Aqua 12 gallon long reef tank. Made my own sump- also have about a 70-100 gallon skimmer on the tank.
2 kessils A150w - about maybe 13-17 pounds of live rock and about 10 pounds of live sand.
a couple fish in there that im going to transfer when to my 55 when they get bigger
All my fish are happy doing fine not one of them seems sick or unhappy.
But every coral I put in this tank just dies..
The parameters seem good too
0 Nitrates
.25 ppm phosphates
500 mg/L ( ppm) Calcium
KH conversion 9

Had the tank up for about 8 weeks now..