I would assume it could read a bit low, but it is easy enough to test. Mix a small batch with RO water to a known concentration and test it.
1% = 10,000 ppm
So 3% = 30,000 ppm
If we want a 1 ppm test solution, we need a 30,000:1 dilution from ammonia in RO water.
First, take exactly 1 mL of ammonia and add it to 99 mL of RO water.
You now have a stock solution of 300 ppm ammonia.
Next, take 1 mL of that solution and add it to 299 mL of RO water.
You now have a final solution of 1 ppm ammonia.
Make sure you rinse everything between solution one and solution two.
Test it with your kit to verify.
Or save the hassle and spend $10 on a new API test kit.
