Step-by-step how-to
How to test aquarium water (parameters every aquarist must check)
Step-by-step guide to testing aquarium water. Ammonia, nitrite, nitrate, pH, alkalinity, calcium, magnesium - which to test, frequency, target ranges.
Beginner8 steps15 min
Step-by-step
Step 1: Take a representative water sampleUse a clean glass cup (not the test kit vial - it has residue). Sample from mid-tank, not surface or substrate. Tap water is testable too if you want a baseline.
Step 2: Test ammonia (NH3/NH4+)Target: 0 ppm. Add reagents per kit instructions. Compare color to chart in proper lighting (daylight or daylight bulb). Any reading above 0 = problem; do partial water change immediately.
Step 3: Test nitrite (NO2-)Target: 0 ppm. Same protocol. Detectable nitrite + low ammonia = mid-cycle. Detectable nitrite + ammonia = cycle hasn't started.
Step 4: Test nitrate (NO3-)Target: reef 5-10 ppm, FOWLR/FW 10-20 ppm. Above 40 = water change needed. Above 80 = parameter-shock risk for sensitive species.
Step 5: Test pHTarget: reef 8.0-8.4, FW 6.5-7.5 (varies by species). Stable pH matters more than perfect pH; daily swings stress fish.
Step 6: Test alkalinity (reef tanks)Target: 8-9 dKH.
Salifert or
Hanna alkalinity checker. Test 2x weekly during initial dial-in, weekly thereafter. Daily swing >1 dKH triggers RTN in SPS.
Step 7: Test calcium + magnesium (reef tanks)Calcium target: 420-450 ppm. Magnesium target: 1300-1400 ppm. Test calcium weekly, magnesium monthly.
Step 8: Log the resultsDate + time + each reading. Track over weeks - trends matter more than single readings. Free apps: Aquarimate, Reef Status, Apex Fusion (if you have an Apex).
Frequently asked questions
How often should I test my aquarium?
New tank: every 3 days during cycling. Established tank: weekly for full panel. Reef tank: 2x weekly for alkalinity during dosing dial-in.
Are API test kits accurate?
API Master Test Kit is accurate for ammonia + nitrite + pH within a reasonable margin. For reef-tank precision (alk swings, phosphate at 0.05 ppm), Salifert + Hanna are more reliable.
Why does my pH keep dropping?
CO2 buildup (closed room, no surface agitation), low alkalinity, or organic acids from a maturing tank. Increase aeration; verify alk; check for old detritus pockets.