Water test results explained

This guide lists every reading Water Check and the Tank Builder's Water test tab look at, the exact cutoffs for each color, the result you'll see, and the fix it suggests. Both tools use the same thresholds.

What are the result levels?

Every graded reading lands in one of four levels:

• Needs action (red): a danger level. Act now.
• To watch (amber): a warning. Not an emergency, but act soon.
• Heads-up (blue on Water Check, gray in the Tank Builder): at the edge of the normal range. Usually nothing urgent.
• Healthy (green): a good reading.

The overall banner is red if anything is red, amber if anything is amber, and green otherwise. Heads-up notes alone never turn the banner amber; on Water Check they change it to "Looking good, a couple of notes."

Quick reference: every threshold

In the Tank Builder only, pH and temperature outside the range your fish share also add an amber result. See the section on fish-fit checks.

What do my ammonia results mean?

Ammonia is entered in ppm. It should be zero.

• 0 ppm: "Ammonia is at zero" (healthy). Your biological filter is keeping up with the waste your fish produce. How to fix: "Nothing to do, keep up your regular maintenance."
• Above 0 but under 0.25 ppm: "Traces of ammonia" (to watch). Ammonia is toxic even at low levels. A trace usually means the tank is still cycling, you're feeding a bit much, or the filter took a hit. How to fix: do a 25-50% water change with dechlorinated water, ease off feeding for a day or two, and hold off adding fish until it reads zero.
• 0.25 ppm or more: "Ammonia is too high" (needs action). At this level it's actively stressing or chemically burning your fish, usually from an uncycled new tank, overstocking or overfeeding. How to fix: do a large (50%) water change right now with dechlorinated water, and another tomorrow if it's still high. Stop feeding for a couple of days, add no fish, and a bottled beneficial-bacteria supplement can speed the cycle.

On most liquid kits the first color above zero is 0.25 ppm, so any color other than zero will read as needing action.

What do my nitrite results mean?

Nitrite is entered in ppm. It should be zero.

• 0 ppm: "Nitrite is at zero" (healthy). The second stage of your cycle is working; together with zero ammonia, that's a healthy, cycled tank. How to fix: "Nothing to do here."
• Above 0 but under 0.25 ppm: "Traces of nitrite" (to watch). Nitrite is still toxic; it stops fish blood from carrying oxygen. It usually means a tank that's mid-cycle or a filter that was recently disturbed. How to fix: do a 25-50% water change, hold off on feeding and new fish, and give the filter time. The cycle is done when ammonia and nitrite both sit at zero.
• 0.25 ppm or more: "Nitrite is too high" (needs action). It's suffocating your fish, so you may see them gasping near the surface. The tank isn't fully cycled, or the filter has crashed. How to fix: large (50%) water change now, and again tomorrow if needed. Stop feeding, add no new fish, and consider a beneficial-bacteria supplement.

What do my nitrate results mean?

Nitrate is entered in ppm. It builds up between water changes, so lower is better.

• 20 ppm or less: "Nitrate is in a healthy range" (healthy). The harmless end product of the cycle, and yours is low. How to fix: "Nothing to do, your water-change routine is working."
• Above 20, up to 40 ppm: "Nitrate is creeping up" (heads-up). Far less toxic than ammonia or nitrite, but a water change is due. How to fix: a 25-30% water change brings it down; live plants also soak up nitrate.
• Above 40, up to 80 ppm: "Nitrate is high" (to watch). Sustained high nitrate stresses fish and fuels algae, usually from overdue water changes, overstocking or heavy feeding. How to fix: do a 30-50% water change now, then get on a regular weekly schedule. Easing off feeding and adding live plants both help.
• Above 80 ppm: "Nitrate is very high" (needs action). High enough to make fish chronically unwell. It needs to come down gradually, because one huge change can shock fish. How to fix: do a couple of 30% changes a day or two apart rather than one massive one, then commit to weekly changes, and check whether the tank is overstocked or overfed.

What do my pH results mean?

pH has no unit. Water Check only flags general extremes, because the right pH depends on your fish. pH never reaches the red "needs action" level.

• 6.5 to 7.8: "pH is in a comfortable range" (healthy). Suits a broad range of community fish. How to fix: nothing needed; avoid chasing a "perfect" number with chemicals, since a stable pH beats a textbook one.
• 6.0 up to (not including) 6.5: "pH is on the soft, acidic side" (heads-up). Ideal for soft-water fish like tetras, rasboras and most South American species, a bit low for livebearers and African cichlids. How to fix: nothing urgent. If your fish prefer harder water, raise it slowly with a little crushed coral, and check your KH.
• Above 7.8, up to 8.4: "pH is on the hard, alkaline side" (heads-up). Great for livebearers, goldfish and African cichlids, a bit high for tetras and many catfish. How to fix: nothing urgent. Driftwood or peat lower it gently over time; avoid sudden chemical swings.
• Below 6.0: "pH is on the low (acidic) side" (to watch). Can stress fish that prefer neutral or hard water, and very low readings can stall your biological filter. Often caused by soft tap water, driftwood or low KH. How to fix: adjust slowly. A little crushed coral in the filter raises it gently; check your KH too.
• Above 8.4: "pH is on the high (alkaline) side" (to watch). Rough on soft-water fish. Usually hard tap water or rocks or substrate that raise it. How to fix: the easiest fix is matching fish to your water; driftwood or peat lower it gently.

What do my temperature results mean?

Temperature is entered in °F only. Like pH, it's graded against general ranges and never reaches red.

• 72 to 82°F: "Temperature is in a comfortable range" (healthy). A solid temperature for most tropical community fish. How to fix: "Nothing to do, just keep it steady."
• 66 up to (not including) 72°F: "Water is on the cool side" (heads-up). Comfortable for goldfish, cool for many tropicals. How to fix: if you keep tropicals, nudge a heater up toward 76-78°F a degree at a time; coldwater setups are fine as they are.
• Above 82, up to 86°F: "Water is on the warm side" (heads-up). Fine for many fish, but warm water holds less oxygen, so watch for fish hanging near the surface. How to fix: no action needed unless fish look stressed; to cool it, go gradually (a fan across the surface helps more than ice).
• Below 66°F: "Water is cold" (to watch). Most tropical fish slow down, stop eating and get more disease-prone; goldfish are fine. How to fix: for tropicals, add or turn up a heater and raise it a couple of degrees at a time toward 76-78°F.
• Above 86°F: "Water is hot" (to watch). Warm water holds less oxygen and speeds up metabolism. How to fix: cool it gradually with a fan across the surface, a partial cooler-water change, or lifting the lid. Sudden swings are worse than the heat.

The Water Check hint under the box says "most like 74-80," which is a narrower suggestion than the healthy band above; anything from 72 to 82°F is graded healthy.

What do my KH results mean?

KH (carbonate hardness, entered in dKH) is your water's buffer: it keeps pH steady.

• Below 3 dKH: "Low carbonate hardness, pH can swing" (heads-up). pH can drift or crash between water changes, which is harder on fish than a stable "wrong" pH. How to fix: a small amount of crushed coral in the filter, or a pinch of baking soda, raises KH and steadies your pH. Go slowly and re-test.
• 3 dKH or more: no result at all. It isn't listed as healthy, it simply isn't shown.

Does Water Check grade GH?

No. GH (general hardness, entered in dGH) doesn't produce any result, in Water Check or in the Tank Builder. The hint under the box ("Soft 4-8, hard 8-12") is just a guide. You can still enter GH so it's recorded with readings you log in the Tank Builder. The Tank Builder doesn't compare GH against your fish either.

What are the fish-fit checks in the Tank Builder?

The Tank Builder's Water test tab adds two checks that Water Check can't do, because it knows your fish:

• "pH doesn't match your stocked fish" (to watch): your pH is outside the range all your fish share. It says, for example, "Your reading is 8.0, but the fish you've added overlap best around 6.5-7.5." How to fix: adjust slowly with natural methods (crushed coral to raise, driftwood or peat to lower), or keep fish that already suit your tap water. Steady beats perfect.
• "Temperature doesn't match your stocked fish" (to watch): your temperature is outside the shared range, for example "your fish overlap best between 74-78°F." How to fix: nudge the heater a degree or two at a time until you're inside that range.

These only appear when you've added fish with pH or temperature data and those fish actually share a range. If your fish don't overlap at all, there's no fish-fit result (the Compatibility tab flags that instead). When you haven't added fish, the tab reminds you: "Add fish and the pH and temperature checks will also tell you how well your water suits them."

Why does my reading show "Nothing to flag from what you've entered"?

That message appears in the Tank Builder's Water test tab when you've entered something but none of it produces a result, for example only GH, or a KH of 3 or more. On the Water Check page the same situation shows a green Your water looks healthy banner with no cards. Either way, nothing was actually graded. Add ammonia, nitrite, nitrate, pH or temperature.

Common problems

Water Check says my ammonia is "at zero" but I typed a negative number. Any value of zero or below is treated as zero. Re-check what you typed.

My pH is 8.6 and it's only amber. pH and temperature never reach red on their own; they top out at "to watch." Still follow the fix, and check the fish-fit result in the Tank Builder.

My nitrate is exactly 20 or exactly 40. 20 counts as healthy. 40 counts as a heads-up ("creeping up"). 80 counts as "high" (amber); only above 80 is red.

My kit shows a range, like 0.25 to 0.5. Enter the value your color matches best. When in doubt, enter the higher number to be safe.

I use test strips that give ppm hardness. Divide the ppm number by about 17.9 to get dGH or dKH.

Why don't I get a green result for KH? KH only produces a result when it's low. A KH of 3 or more simply shows nothing.