20 gallon long, 9" comet and 2" common (9" being rehomed today in a 200 gal*, 2" staying to complete cycle). Minimal feeding (they're hungry), 10-15% wc daily w/gravel vac, using Prime to treat tap water. Prime converts deadly ammonia (NH3) to tolerable ammonium (NH4), right? And the API master test kit does not discriminate between them, so a post-Prime test shows no reduction in ammonia, even if it's all been converted to ammonium, right? (Still learning the basics and need when correction if I have it wrong). Test this mornings pre-wc and Prime dose was ammonia was somewhere between .25 and .50, nitrites at 0. Dosed with Prime yesterday morning to knock down a similar ammonia reading. Is yesterdays Prime still active and giving a false ammonia positive, or did it wear off and this morning's reading accurately reflects new ammonia? If I always use Prime to treat the tap water before adding during wc's, do I ever get an accurate read on what's happening? The zero nitrite read is also confusing me. Does that mean I haven't even begun to have some nitrifying bacteria set up shop, or did yesterday's Prime affect this mornings reading? Thank's for any advice on how to proceed analyzing this. * PS The 9" comet is going back to live where he has for the last five years, a galvanized horse stock tank at another location. Tested the water still in it, ammonia 0, nitrites 0, phosphates 0, pH 8 (same as tap), my kit for koi lacks a nitrate test, fixing today. I expect no issues, the tanks temp by afternoon is the same as my home tank he's in now, 62.