What needs testing and how often
Test frequency depends on system age and stability. New systems demand daily testing during cycling. Established freshwater community tanks need weekly nitrate at most. Established SPS reef tanks demand a structured weekly + biweekly + monthly + quarterly schedule.
Freshwater testing matrix
- Cycling phase: ammonia, nitrite, nitrate, pH daily for 4-8 weeks
- Established community: nitrate weekly, pH and KH monthly
- Planted high-tech: nitrate, phosphate, KH, pH (CO2 indicator), iron, GH biweekly
- Caridina shrimp: TDS weekly, GH and KH biweekly, pH monthly, ammonia/nitrite when adding stock
- Cichlid (African): pH and KH weekly, nitrate biweekly, GH monthly
- Discus / Apistogramma: nitrate weekly, pH biweekly, GH and KH monthly, TDS monthly
Saltwater testing matrix
- Cycling phase: ammonia, nitrite, nitrate, pH daily for 6-10 weeks
- FOWLR established: nitrate, salinity weekly; pH, alk, ca monthly
- Soft / LPS reef: alk, ca, mg, salinity, pH weekly; nitrate, phosphate biweekly
- SPS reef (the demanding tier): alk, ca, salinity, temp daily ideally (digital monitors); mg, nitrate, phosphate weekly; ICP quarterly
Test kit comparison (saltwater focus)
Alkalinity
| Kit | Cost | Accuracy | Notes |
|---|
| API KH | $8 | Low (1.0 dKH error) | Beginner only |
| Salifert KH | $22 | Good (0.2 dKH) | Hobby standard |
| Hanna Marine ULR | $70 + $25/yr reagent | Excellent (0.05 dKH) | Digital, fast |
| Red Sea KH Pro | $30 | Very good (0.1 dKH) | Color comparison |
| Trident (Apex) | $1,000+ | Excellent | Auto-tester, 4 daily readings |
Calcium
- API Calcium: $9, ~30 ppm error, beginner only
- Salifert Calcium: $25, ~20 ppm error, hobby standard
- Hanna Marine Calcium: $70, ~5 ppm error, digital
- Red Sea Calcium Pro: $30, ~15 ppm error, color comparison
Magnesium
- Salifert Magnesium: $30, ~30 ppm error, standard choice
- Red Sea Magnesium: $30, ~25 ppm error
- Hanna Marine Magnesium: $70, ~10 ppm error
Nitrate (the trickiest)
API and Red Sea Nitrate kits read inaccurately at the low end (under 5 ppm). For SPS reefkeeping where you care about 1-5 ppm, you need a low-range option:
- API Nitrate: $9, useless under 10 ppm, fine for FOWLR
- Red Sea Nitrate Pro: $30, decent above 2 ppm, hobby standard
- Hanna Marine ULR Nitrate: $90 + $30/yr reagent, accurate to 0.5 ppm, SPS standard
- NYOS Nitrate: $35, excellent low-range
- Salifert Nitrate: $30, mid-range (5-25 ppm) accurate
Phosphate (also tricky)
- Hanna ULR Phosphate (HI-736): $50, 0.01 ppm precision, the SPS standard. Buy this one.
- Hanna LR Phosphate: wider range but coarser, FOWLR or LPS-only
- Salifert / NYOS: color-comparison, useful but less precise than digital
Salinity / specific gravity
- Hydrometer: $5, inaccurate by 0.001-0.003 SG. Replace.
- Refractometer (manual): $30, accurate when calibrated against 35 ppt calibration solution. Hobby standard.
- Digital refractometer (Milwaukee, Hanna): $200, easier to read, same accuracy as good manual.
- Conductivity probe (Apex, Neptune): $300+, continuous monitoring, requires calibration every 6 months.
Digital monitors and continuous testing
The Apex / Neptune ecosystem
Apex is the standard reef controller. Modules add capability:
- Apex base: ~$700, includes pH, ORP, temperature, salinity probes
- PMUP (peristaltic dosing): per-module ~$200, multi-channel dosing
- Trident: $1,000+, auto-tests alk, calc, mg up to 4x daily
- Apex DOS: $300, four-channel dosing pump
- WAV pumps: Apex-controlled flow pumps
Trident replaces manual alk/calc/mg testing for SPS reefers. The annual reagent cost is ~$300 but the data quality (4 daily readings vs 1-2 weekly) is transformative for parameter discipline.
Hydros (the Apex challenger)
Cheaper, simpler, more limited. Good for soft/LPS reefers who want some automation without Apex's full ecosystem.
Reef-Pi (the open-source option)
Raspberry Pi-based reef controller, free software, requires DIY hardware integration. For developers and tinkerers, a tenth the cost of Apex with similar capability.
ICP-OES testing (the quarterly truth check)
ICP-OES (inductively coupled plasma optical emission spectrometry) is the laboratory technique for measuring 30+ elements simultaneously in a water sample. Hobby-grade ICP services produce a quarterly report covering trace elements your hobby kits cannot detect.
What ICP catches that hobby kits miss
- Trace metal contamination: copper from leaching pipes, iron from substrate, zinc from heaters
- Trace element depletion: iodine, strontium, vanadium, lithium, manganese, molybdenum
- Salt mix variability: different brands produce different trace profiles
- Long-term drift: what your tank has slowly accumulated or lost over months
ICP service comparison
- Triton ICP-OES (Germany): $40-50 per test, the original. Pairs with Triton dosing methodology. 2-week turnaround typical.
- ATI Labfish (US): $35-45 per test, US shipping faster.
- Aquabiomics (US): $40-60 per test, also offers microbiome analysis.
- Reefmoonshiners: $30-40, hobby-priced, German-based.
Run ICP quarterly during your first year. After you understand your tank's trace profile, semi-annually is sufficient unless you're pushing parameters or seeing issues.
When test kits lie
Calibration drift
Pinpoint pH and ORP probes drift 0.1-0.3 units over 3-6 months. Calibrate quarterly with fresh standards. Refractometers drift if knocked or if calibration solution is old.
Reagent expiration
Salifert and Red Sea reagents have 1-2 year shelf life. Hanna reagents 6-12 months. Old reagents read low across the board. Date your kits.
Operator error
The most common test error is the reefer. Sloppy syringe technique, mixing reagents in wrong order, reading at wrong temperature. Run the same sample twice if a result surprises you.
Sample contamination
Use the same sample container for the same test. Rinse with RO/DI between uses. Avoid touching the inside of the container.
Time-of-day effects
pH swings 0.2-0.4 units between dark and lights-on (CO2 from photosynthesis vs respiration). Test at the same time each day for trend tracking. Alkalinity is more stable but still consumed during peak photosynthesis hours.
The recommended SPS testing kit
If you're starting an SPS reef and want one consolidated buying list:
- Hanna Marine ULR Alkalinity (HI-772) - $70
- Hanna Marine Calcium (HI-758) - $70
- Hanna ULR Phosphate (HI-736) - $50
- Hanna ULR Nitrate (HI-781) - $90
- Salifert Magnesium - $30
- Refractometer + 35 ppt calibration solution - $40
- Digital pH probe (Apex / Hydros / standalone) - $50-200
- Quarterly ICP from Triton or ATI - $40-50
Total: ~$400-500 startup, ~$200/yr reagent. This kit handles every parameter that matters for SPS keeping with hobby-leading accuracy.
Tracking your data
Test results without trend tracking are wasted. Three options:
- Apex Fusion: auto-logs probe data, manual entry for kit results
- Reef Calendar / spreadsheet: manual but flexible
- Aquatic Log app: mobile-friendly, includes graphing
Track at minimum: alkalinity, calcium, magnesium, salinity, nitrate, phosphate, temperature. Plot weekly. Notice the trend lines before parameters cross dangerous thresholds.