What’s in the kit?
The API Freshwater Master Test Kit tests pH, high-range pH, ammonia, nitrite and nitrate. Those are the readings for cycling a new tank and for checking the water when fish look unwell. It does not test general hardness (GH), the calcium and magnesium dissolved in the water, or carbonate hardness (KH), the buffering that holds pH steady; a separate kit such as API’s GH & KH kit covers both, and low KH is a common reason for a pH that drifts.
Strips read several things in about a minute: API’s 5-in-1 and Tetra’s 6-in-1 include GH and KH but have no ammonia pad, so ammonia comes on its own strip or in a liquid kit. If you dose Prime or another ammonia binder, Seachem’s MultiTest Ammonia reads the free ammonia, the toxic part, separately from the total.
Check the exact kit’s test list on its test kit page before you buy; a box called “master” still covers only the tests printed on it. Once you have readings, see what each one means for your fish.
Range, steps and accuracy
Read results against the color chart that came with your kit, in daylight or bright white light. The chart covers a range in steps (for example 0, 0.25, 0.5 and 1 ppm of ammonia); a color between two steps means a reading somewhere between them. A home kit is a good guide, not a lab measurement. If you need to know how low a kit can detect, its instructions say. A phone photo of a test tube shifts the colors, so judge the tube itself, not a picture of it.
Each test has its own steps
Each test in a kit has its own sample size, number of drops, shaking and waiting time, and some ask you to shake a bottle hard before adding it. Follow the card for each test rather than one routine for all of them, rinse the tubes with tank water before and clean water after, and read the color at the time the card gives. Keep the instructions with the kit.
Keep a test log
Write down the date, what you tested, the result and anything you did, such as a water change or new fish. A log shows a reading creeping up long before one test looks alarming; the cycling log keeps one in your browser. Reagents expire and run out, so note the dates on the bottles and count refills in your first-year cost.
What a test can’t tell you
Good readings show the water is safe today. They do not show that a tank has room for more fish, that the fish will get along, or that a sick fish will recover. For stocking, use the stocking checker; for a fish that looks unwell, test first, then match the symptom, and ask a vet who treats fish if it does not improve.
Each reading in detail: ammonia · nitrite · nitrate · pH · GH · KH.