Your phosphate level if the culprit for stunted to no growth. GFO or water change ...if you nitrates are zero, any of the biopellets will not work.
On the other hand, I trust salifert for advanced tests (ca, mg, co3, phosphate) and API for basics (ammonia, nitrite, nitrate). Some of the other tests, especially Red Sea is notorious for reagents going bad over period of time. The problem is you don't know when to stop trusting the test kit or fix the issue.