Using Water Check

Water Check reads your aquarium test kit numbers and tells you, in plain English, what's healthy, what isn't, and how to fix it. It's free, needs no account, and nothing you type is saved. For advice matched to the fish you keep, or to keep a history of readings, use the Water test tab in the Tank Builder instead.

How do I check my water?

1. Open Water Check (it's also in the Tools menu as "Water Check: Read your test results").
2. Test your water with your kit or strips.
3. Type each result into its box under Your reading. Fill in only what you have; you don't need every box.
4. Results appear instantly beside the form on wide screens, or below it on phones. There's no submit button.

To start over, tap Clear at the top right of Your reading. It empties every box.

What boxes are on the Water Check form?

The form is split into three groups. Each box shows a sample value as a placeholder and a quick guide underneath.

Temperature & pH ("The basics, comfort and acidity.")

• Temperature in °F. Guide: "Safe 66-86°F · most like 74-80"
• pH (no unit). Guide: "Safe 6.0-8.4 · ideal varies by fish"

The nitrogen cycle ("Fish waste turns to ammonia, then nitrite, then nitrate. This is where most trouble shows up.")

• Ammonia in ppm. Guide: "Should be 0"
• Nitrite in ppm. Guide: "Should be 0"
• Nitrate in ppm. Guide: "Keep under 20"

Hardness ("How mineral-rich your water is, and how stable your pH stays.")

• GH in dGH. Guide: "Soft 4-8, hard 8-12"
• KH in dKH. Guide: "3+ keeps pH steady"

You can type decimals in any box (for example 0.5 for ammonia or 7.4 for pH). The arrow buttons on each box step by 1 for temperature, GH and KH, 0.1 for pH, 0.25 for ammonia and nitrite, and 5 for nitrate.

What units does Water Check use?

• Temperature: degrees Fahrenheit only. If your thermometer reads Celsius, multiply by 9, divide by 5 and add 32 (25°C is 77°F).
• Ammonia, nitrite, nitrate: ppm (parts per million). Kits that read in mg/L give the same number.
• GH: dGH (degrees of general hardness). KH: dKH (degrees of carbonate hardness). If your kit reports hardness in ppm, divide by about 17.9 to get degrees.
• pH: no unit.

There's no switch for Celsius or other units, so convert before typing.

What does the summary banner mean?

Once you fill in at least one box, a banner at the top of the results sums up your water:

• Needs attention now (red): "Something in your water is stressing your fish, see the steps below." At least one value is in the danger zone.
• A few things to watch (amber): "Not an emergency, but worth acting on soon." At least one value needs attention, but nothing is dangerous.
• Looking good, a couple of notes (green): "Nothing's wrong. A few values sit at the edge of the ideal range, details below." Nothing is wrong, but something sits at the edge of normal.
• Your water looks healthy (green): "Everything you entered is in a good range. Keep it up."

Under the banner, small counters show how many results are in each level, for example "1 needs action," "2 to watch," "1 heads-up," "3 healthy."

What do the colors mean?

Water Check uses four levels, and the same colors appear on the result cards, the counters, and the input boxes:

• Red (needs action): a danger reading, like ammonia or nitrite at 0.25 ppm or more, or nitrate over 80 ppm.
• Amber (to watch): a warning, like a trace of ammonia, nitrate over 40 ppm, pH outside 6.0 to 8.4, or temperature outside 66 to 86°F.
• Blue (heads-up): an edge-of-normal note, like nitrate between 21 and 40 ppm, pH at the soft or hard end of normal, a slightly cool or warm tank, or low KH.
• Green (healthy): a good reading.

Every threshold is listed in Water test results explained.

How do I read the result cards?

Anything that isn't healthy gets its own card, sorted most urgent first (red, then amber, then blue). Each card shows:

• A title, for example "Traces of ammonia" or "Nitrate is creeping up"
• The value you entered, on the right, for example "0.1 ppm"
• What's happening: a plain-English explanation of what the reading means and the usual causes
• How to fix: what to do about it

Healthy results are listed more briefly under Looking good, each with a green check, its title (like "Ammonia is at zero") and your value.

Why did my input box change color?

After you type a value, the box's border and a small dot next to its label change color to match that result: red, amber, blue or green. This lets you see at a glance which number is the problem.

Two boxes behave differently:

• GH never changes color because Water Check doesn't grade GH on its own.
• KH stays uncolored even when it's low. A low KH still shows up as a blue heads-up card in the results, so look there.

Which readings does Water Check give results for?

Water Check gives a result for ammonia, nitrite, nitrate, pH and temperature every time you enter them. For KH, you only get a result if it's below 3 dKH (a blue heads-up that your pH may swing); 3 or above gives no card at all. GH never gives a result. You can still enter it, and it's saved with readings you log in the Tank Builder.

If the only thing you entered is GH (or a KH of 3 or more), the banner will still say Your water looks healthy even though nothing was actually graded. Enter ammonia, nitrite, nitrate, pH or temperature for a real read.

Why does Water Check say my pH or temperature is fine when my fish need something else?

Water Check doesn't know what fish you keep, so it only uses general safe ranges that suit most community fish. A pH of 7.6 is "comfortable" for most tanks but too high for some soft-water fish, and 70°F is fine for goldfish but cool for tropicals.

For advice matched to your fish, open the Tank Builder, add your fish, and use its Water test tab. It adds two extra checks, "pH doesn't match your stocked fish" and "Temperature doesn't match your stocked fish," and tells you the range your fish share. The link at the bottom of Water Check, Keeping fish? Use the Tank Builder for checks tailored to your stock, takes you there.

Is anything I type into Water Check saved?

No. Water Check doesn't store your numbers anywhere, even if you're signed in. Refreshing or leaving the page clears the form. To keep a history of your water tests, log them from the Water test tab of the Tank Builder while signed in. See Logging water tests.

Do I need an account to use Water Check?

No. Water Check works the same for everyone, signed in or not. You only need an account to log readings to a saved tank in the Tank Builder.

How often should I test my water?

Water Check doesn't set a schedule or send reminders. Its advice mentions testing again after a fix (for example, doing another water change "tomorrow if it's still high," or re-testing after raising KH). If you log readings in the Tank Builder, logging at least once each week earns you bubbles. See Logging water tests.

What's the difference between Water Check and the Tank Builder's Water test tab?

Both use the same thresholds and the same result text. The differences:

• Water Check (/water-check): general safe ranges only, per-box hints, colored input boxes, results sorted by urgency with healthy ones grouped under Looking good, and a Clear button. Nothing is saved.
• Tank Builder Water test tab: knows your fish, so it adds the two fish-fit checks for pH and temperature. Signed in, you can log readings to a saved tank and see your recent history. Its banner wording is a little different ("Something needs attention now," "A few things to keep an eye on," "Your water looks healthy"), it lists every result as a card in a fixed order, and heads-up notes show in gray.

Common problems

Nothing shows in the results. Fill in at least one box. Until then you'll see "Enter a reading to begin. Fill in at least one value and your results appear here." If you typed something that isn't a number, it's ignored.

My kit reads 0.25 ppm ammonia and Water Check says "Needs attention now." That's correct. Any ammonia or nitrite at 0.25 ppm or above is treated as needing action, and on most kits 0.25 is the first color above zero. Follow the How to fix steps.

My thermometer reads Celsius. Water Check only takes °F. Multiply by 9, divide by 5 and add 32 before typing.

I entered GH and got no result. GH isn't graded on its own. It's there so you can record it when logging in the Tank Builder.

The banner says healthy but I only entered GH. With nothing gradeable entered, there's nothing to flag. Add ammonia, nitrite, nitrate, pH or temperature for a real read.

My KH box didn't turn blue even though KH is low. The KH box doesn't change color. Your low KH result appears as a blue heads-up card in the results list.

My numbers disappeared. Water Check never saves your entries. Log them in the Tank Builder if you want to keep them.