Do you know the names of the corals you've been unsuccessful with?
What did you see when they died?
What kind of lighting do you have?
Did you test the water the corals came from?
It may or may not matter but what is your Mag @?
API kits can be unreliable when trying to get exact and consistent readings.
Consider Salifert or Red Sea, with a Hanna ULR for PO4
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