Understanding Your ICP Test Results: A Reef Keeper's Guide
Learn how to interpret ICP lab reports for your reef tank. Understand element categories, identify problems, and take action on your results.
ICP (Inductively Coupled Plasma) testing gives you a detailed snapshot of your reef tank’s water chemistry—far beyond what standard test kits can measure. But those lab reports can be overwhelming. In this guide, we’ll break down how to interpret your ICP results and take action.
What Is ICP Testing?
ICP-OES (Optical Emission Spectroscopy) is a laboratory technique that can measure 30-60+ elements in a single water sample. Unlike home test kits that measure one parameter at a time, ICP testing reveals:
- Major elements like calcium, magnesium, and potassium
- Trace elements that affect coral health and coloration
- Nutrients including nitrate and phosphate
- Pollutants that may be harming your tank
Popular ICP labs for reef keepers include ATI, Triton, and Fauna Marin.
How to Read Your Results
ICP reports typically show three columns:
- Your Value - What was measured in your sample
- Reference Range - What’s considered “normal” for reef tanks
- Status - Whether you’re in range, high, or low
Let’s break down the elements by category.
Major Elements
These are present in significant quantities and essential for reef chemistry.
Calcium (Ca)
Target: 400-450 ppm
The primary building block of coral skeletons. Your ICP result should match what you measure at home with a quality test kit. If there’s a big discrepancy, check your home test kit’s accuracy.
Magnesium (Mg)
Target: 1280-1380 ppm
Prevents calcium/alkalinity precipitation. ICP is excellent for verifying your magnesium level, as home kits can be less accurate.
Potassium (K)
Target: 380-420 ppm
Often overlooked but important for coral health and coloration. Low potassium can cause slow tissue necrosis (STN) in some corals. If low, potassium supplements are available.
Strontium (Sr)
Target: 8-10 ppm
Incorporated into coral skeletons alongside calcium. Usually maintained through water changes and quality salt mixes.
Boron (B)
Target: 4.5-5.5 ppm
Important for pH stability and coral health. Typically stable if using quality salt.
Trace Elements
Present in smaller amounts, these affect coral coloration, growth, and overall health.
Iodine (I)
Target: 0.04-0.06 ppm
Important for soft corals, invertebrate molting, and some coral coloration. Consumed fairly quickly in active tanks.
Iron (Fe)
Target: 0.002-0.01 ppm
Essential for macroalgae growth in refugiums. Most reef tanks have adequate iron from feeding.
Zinc (Zn)
Target: 0.002-0.01 ppm
Trace amounts needed, but excess can be toxic. Often elevated if using galvanized equipment.
Manganese (Mn)
Target: 0.0003-0.003 ppm
Required in tiny amounts. Rarely an issue unless supplementing.
Nutrients
Nitrate (NO3)
Target: 1-10 ppm (varies by methodology)
Your ICP nitrate should roughly match home testing. Note that some labs measure nitrogen (N) rather than nitrate (NO3)—the conversion factor matters.
Phosphate (PO4) / Phosphorus (P)
Target: 0.02-0.1 ppm phosphate
Some labs report phosphorus (P), others report phosphate (PO4). Know which your lab uses:
- To convert P to PO4: multiply by 3.066
- To convert PO4 to P: divide by 3.066
Pollutants: The Red Flags
This is where ICP testing really shines. These elements should be as low as possible.
Aluminum (Al)
Limit: Less than 5 ppb
Common sources:
- GFO (granular ferric oxide) media
- Some live rock
- Tap water
Action: If elevated, replace GFO with a different brand, check your source water, and do water changes with clean saltwater.
Copper (Cu)
Limit: Less than 5 ppb (toxic to invertebrates)
Common sources:
- Old plumbing/pipes
- Copper-based medications
- Some supplements
Action: Copper is extremely toxic to invertebrates. Run Cuprisorb or similar media. Never use copper medications in a reef tank.
Lead (Pb)
Limit: Less than 5 ppb
Common sources:
- Old solder joints
- Some equipment
- Contaminated source water
Action: Investigate equipment and plumbing. Remove any suspect items. Run chemical media.
Tin (Sn)
Limit: Less than 2 ppb
Common sources:
- Some supplements (especially low-quality trace element mixes)
- Soldered equipment
Action: Stop suspicious supplements. Check for corroding equipment.
Zinc (Zn)
Limit: Keep low (under 10 ppb)
Common sources:
- Galvanized metal (clamps, screws, etc.)
- Some lower-quality equipment
Action: Remove all galvanized metal from your system. This is a common source.
What to Do With Your Results
If Everything Looks Good
Congratulations! Your water chemistry is balanced. Continue your current maintenance routine and test again in 2-3 months to track trends.
If Major Elements Are Off
- Adjust dosing to correct calcium, magnesium, or potassium
- Make changes gradually over days, not hours
- Re-test with home kits to verify correction
If Trace Elements Are Low
- Consider a quality trace element supplement
- Increase water change frequency/volume
- Check your salt mix specifications
If Pollutants Are Elevated
- Identify the source - Check equipment, media, supplements
- Remove the source - This is critical
- Run chemical filtration - Activated carbon, Cuprisorb, Polyfilter
- Do water changes - Dilute existing contamination
- Re-test - Verify levels are dropping
ICP Testing Best Practices
- Test consistently - Same time relative to water changes
- Avoid contamination - Use clean containers, don’t touch the sample
- Include reference water - Some labs offer this for comparison
- Track over time - One test is a snapshot; multiple tests show trends
- Combine with home testing - ICP supplements, doesn’t replace, regular testing
How ReefTanker Helps
Manually tracking ICP results is tedious. ReefTanker lets you:
- Upload ICP PDFs and automatically extract all element values
- View results organized by category (major, minor, nutrients, pollutants)
- Track trends across multiple tests
- Get alerts when pollutants exceed safe levels
Try ReefTanker to make sense of your ICP data and track your reef chemistry over time.
Conclusion
ICP testing is a powerful tool for understanding your reef tank at a deeper level. Focus on the major elements and pollutants first—they have the biggest impact on coral health. Track your results over time to spot trends before they become problems.
Remember: the goal isn’t perfect numbers, but stable chemistry and the ability to identify issues early.