Water Quality Calculator

Only the un-ionized fraction of total ammonia (NH3) is meaningfully toxic to fish gills; the rest exists as the far less harmful ammonium ion (NH4+). The chemical equilibrium between the two forms shifts toward the toxic NH3 form as pH rises, so a TAN reading of 1 ppm might be mostly safe ammonium at pH 6.5 but mostly toxic NH3 at pH 9. This calculator converts your raw TAN reading into estimated un-ionized ammonia using pH and temperature before judging it, rather than treating all ammonia readings the same regardless of pH.

Warm water holds less dissolved oxygen at saturation than cold water, so the same ppm reading represents a smaller share of what the water could hold when it is warm. This calculator reports both the raw ppm and the percent of temperature-adjusted saturation, and a reading that looks numerically adequate in isolation can still represent a stressed, oxygen-depleted condition relative to what that water is capable of holding at its current temperature.

Danger means at least one parameter has crossed a threshold associated with acute fish stress or mortality risk, and it calls for immediate corrective action rather than routine monitoring — for ammonia or nitrite spikes that typically means a partial water change and reduced feeding, for low dissolved oxygen it means increasing aeration immediately. Because un-ionized ammonia toxicity compounds with low oxygen and pH swings, treat a Danger reading as urgent even if only one parameter triggered it, and recheck within hours rather than days.

No — the thresholds built into this calculator are general-purpose midpoints drawn from common finfish culture guidance, not species-specific limits. Cold-water species like trout are markedly more sensitive to low dissolved oxygen and ammonia than warm-water species like tilapia or channel catfish, which can tolerate conditions this calculator would flag as a warning. Always cross-check against species-specific husbandry guidance for the animal you're actually raising before treating any single threshold as a hard rule.

In a stocked, actively-fed system, ammonia and nitrite should be tested at minimum weekly, and daily during startup of a new system or after any stocking density increase, because the nitrogen cycle can lag feed increases by days and spike suddenly. Dissolved oxygen and temperature are cheap and fast to test and are best checked at least daily, ideally near dawn when DO is at its daily low point after a night of respiration with no photosynthesis replenishing it.