So I did a 20% water change last night and tested my water with the API test kit today in the afternoon. My ammonia still read between 0 and 0.25, nitrite 0, an nitrate came down to between 10 and 20ppm. Earlier in the week I ordered a Red Sea ammonia test kit and it arrived an hour ago. After testing ammonia with the Red Sea kit I'm reading 0ppm. So with zero ammonia and zero nitrite I should be clear to add a small CUC, yes?
As you will find, most of us that have been in the hobby for awhile will all tell you that API test kits suck. They are notorious for being inaccurate, and once they get a little age on them, they're
even more inaccurate. Rea Sea, Salifert, and even Elos beat API hands-down. They cost more, and there's a reason... they're superior. The life of your tank depends on one thing... good water parameters. You'll pay more for quality test kits, but you'll actually
save money in the long run as the loss of a fish or two will easily wipe out any savings you may have gotten by buying a cheap test kit.
I was allowing for the variance in API tests, and that's why I suggested doing a water change and testing again. If you had gotten similar results after a water change, then you would know that it was an error on API's end. However, you'll often get different readings on back-to-back tests using API. Instead of buying a Red Sea Ammonia test, I wish you had bought a Nitrate test. Your tank has cycled, and unless there's a big change to the system, Nitrate will be all you need to test for on a regular basis. Not saying it's not a good idea to check Ammonia and Nitrite every now and then, but it's not critical. If you stock the tank
slowly to allow the biosystem to adjust to the new load, Ammonia and Nitrite shouldn't be a concern. The only time either of those should be a concern is if there is a death of a large(r) critter and it begins to decay in the tank. This can give a short-term ammonia (and consequently Nitrite) spike... which can be handled with a simple water change if it spikes too high. Normally it will level off fairly quickly on it's own if levels don't go
too high. A good cleanup crew will help reduce spikes caused by a dead critter by eating it before it has a chance to decay. Nassarius snails and hermits are awesome at this task.