i have a 1999 deville and its lossing antifreeze

Hi i have a 1999 cadillac deville and it has where to check the coolint lever and when i did it is low but its not the first them it came on i had the rad.replaced and had it checked too and they can not find anything wrong can anyone tell me what is wrong with it i really like the car the car was pressure checked and they could not find any leaks they said but it still leaks antifreeze

No external leaks? Was the system pressure tested, was the engine checked for head gasket leaks, no meaningful info has been provided here.

No external leaks? Was the system pressure tested, was the engine checked for head gasket leaks, no meaningful info has been provided here.
the car was pressure checked and they said they could not found any leaks but it still leaks anitfreeze

Again, you mean it looses coolant, no visible leaks right? If so there is a test that can be done to check for exhaust gases in the coolant, that would indicate a head gasket issue.

NAPA sells a test kit that you can use to test for exhaust gases in your radiator. That would give you the answer to whether it is one of the head gaskets, or not!
Is coolant getting into the oil?

NAPA sells a test kit that you can use to test for exhaust gases in your radiator. That would give you the answer to whether it is one of the head gaskets, or not!
Is coolant getting into the oil?
the last time i checked and filled the antifreeze the color was kind of black and the garage did put stop leak in it to .do u how much the kit is at napa to check .

It was around $60.

How quickly are you losing coolant? Is it low in a day or a couple of weeks. Headgaskets and their bolts pulling out of the block are common problems with the pre-2004 Nothstars. If it is a slow loss, some common leak points are the water pump housing crossover gaskets, and the quick connect fitting that screws into it. The crossover runs across the top of the trans under the throttle body, connecting the block and head coolant passagaes. Sometime these leak very slow, the coolant residue collects on the trans and is heated and sometimes never hits the ground. Check all around for dried pink residue. If you look under your intake plenum near the power steering pump area (engine cover off) and see oil in the valley, this is a good sign that the headgaskets are leaking.