Testing: The Boring Bit That Matters Most
By the time something looks wrong in a reef tank, the damage is already done. Regular, accurate testing is the difference between a thriving tank and a frustrating one.
The Core Parameters
Test these weekly at minimum:
- Alkalinity (dKH): 7.5–9.5 dKH. The most important parameter for coral health. Consistency matters more than the exact number
- Calcium (Ca): 400–450 ppm. Consumed by stony corals for skeleton building
- Magnesium (Mg): 1250–1400 ppm. Stabilises calcium and alkalinity
- Salinity: 1.025–1.026 SG. Use a refractometer, not a hydrometer
- Phosphate (PO4): 0.03–0.05 ppm is the sweet spot for SPS
- Nitrate (NO3): 1–10 ppm for mixed reef. Zero isn't actually ideal — corals need some nutrients
Beyond the API Kit
The API master test kit is fine for cycling, but the colour-matching cards lack the accuracy needed for ongoing reef keeping. Hanna checkers are the sweet spot — digital readings, no squinting at colour cards:
- HI772 — Alkalinity (~£45). The single best testing upgrade
- HI774 — Ultra-low range phosphate (~£50). Essential for SPS
- Salifert kits — The standard for calcium and magnesium. £8–12 per kit
ICP Testing
ICP-OES is a laboratory analysis testing 30+ elements. Post a sample to Fauna Marin, ATI, or Triton (~£30–40 per test). Useful every 2–3 months, or when troubleshooting unexplained issues.
A Practical Testing Schedule
- Daily: Quick salinity check
- Twice weekly: Alkalinity
- Weekly: Calcium, phosphate, nitrate
- Fortnightly: Magnesium
- Quarterly: Full ICP test
One Important Tip
Always test at the same time of day. Alkalinity especially fluctuates throughout the light cycle. Testing at different times creates misleading data.
Browse test kits and monitoring equipment from UK sellers — barely-used Hanna checkers often come up from reefers who've upgraded to continuous monitoring.
What testing routine works for you? Any kit recommendations?
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