How to Test Your Water | AMT CarbonClear

The testing process

Some laboratories and test kits only test for TOCs (Total Organic Carbon). The difference between Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC) is the DOC water sample is first passed through a 0.45µm filter before analysis.

The goal is to establish a baseline before assuming a problem exists based on a single reading.

Test multiple times on different days, to establish a daily fluctuation range in your specific system. You cannot rely on a single test reading to be an accurate representation of true DOC levels in the system.

Test at the correct time as DOC levels will fluctuate with feeding.

Take one sample right after feeding (near-peak DOC) and one sample just before feeding (near-trough DOC). Log both results.

Take your water sample from the same location each time.

Same tank or system location each time, mid-water column, away from inflow/outflow turbulence. Avoid surface film and dead zones.

Run the colorimetric DOC test kit.

Add reagent, match sample colour against the reference disc/chart, read result directly in mg/L. The same format as the water test kits you’d likely already be familiar with. Alternatively, send your water sample off to a lab to be tested.

Record system context alongside the test result figure.

Feed rate, system age, biofilter maturity, stocking density, water exchange rate, etc all affect DOC accumulation behaviour and levels in your system. A single DOC reading without this context isn’t as informative.

Compare your results against the system’s own trend.

A rising DOC trend over successive tests is a stronger signal than a single reading against a fixed guideline number, given no properly validated RAS-specific DOC harm threshold exists yet.

Characteristics farmers need to know before testing

Timing drives the result more than most farmers would assume. A trough-time sample (before feeding) can look “clean” while a peak-time sample (after feeding) from the same location on the same day shows a very different reading. Testing once, at the wrong time, simply produces an inaccurate reading.
New/high-feed-rate systems and old/low-feed-rate systems behave differently. A young system with a still-maturing biofilter will show different DOC accumulation patterns to an established one. A single farmer’s “normal” isn’t a universal normal.
A single reading can’t be called “harmful” or “not harmful” as no RAS-specific DOC harm threshold exists yet. You should classify your reading as ‘elevated’ or ‘not elevated’ and ‘trending up’ or ‘trending down’.

Suggested Test Kit

Total Organic Carbon (TOC) Reagent Set from Hach
Testing methodology here

DOC reading guideline

Not elevated DOC<5.0mg/L

Elevated DOC>5.0mg/L

Elevated DOC affecting your system?

Try CarbonClear How CarbonClear works