Netlit

A 60 cm tank is not 64.8 litres

Multiply 60 × 30 × 36 cm from the outside and you get 64.8 L. Take away the glass thickness, the real water line, 6 cm of gravel and 3 L of hardscape, and roughly 48 L is left — 26% less.

Yet that outside figure is what most "one third water change" and "x mg per litre" decisions are quietly based on. Netlit settles the number once, then puts every later calculation on top of it.

Net volume, shown as the subtraction it is

Enter the outside dimensions, glass thickness, height of the water line, substrate depth and type, hardscape and equipment, and Netlit shows you the breakdown — what was taken off the gross volume, item by item, to arrive at the net figure.

Every substrate porosity preset is labelled as an estimate. Fired aqua soils in particular vary a lot between products, so the default is provisional and measuring your own by displacement is worth the ten minutes. When the inputs contradict each other — substrate plus hardscape exceeding the gross volume, say — Netlit returns no number and points at the contradiction instead.

Water changes account for what is in your tap water

The concentration after a water change is not set by the current value and the change ratio alone. What the replacement water already contains matters. Nitrate in tap water varies enormously by region, so Netlit ships no default for it and asks you for the figure that applies where you live.

When the source value is at or above your target, no water change will get you there. In that case Netlit does not produce a number. Rather than answering "change x%", it offers the alternatives: cut the source water with RO/DI, or set a different target.

You decide how much is safe in one go

How much water may be replaced at once depends on the tank and its inhabitants. It is not an app's place to assert a figure, so on first launch you set your own ceiling anywhere between 20% and 80%, and can change it later in settings.

The safety indicator does not look only at the change ratio. It also compares the temperature, pH, KH and TDS of the old and new water, and whenever it raises a caution or a warning it states the reason in words.

Dry salts, with the ions that come along

Potassium nitrate (KNO₃), monopotassium phosphate (KH₂PO₄), potassium sulphate (K₂SO₄) and magnesium sulphate heptahydrate (MgSO₄·7H₂O) are supported in both directions: how much a given dose raises the concentration, and how much salt a target rise needs.

Dose KNO₃ to raise nitrate and you raise potassium at the same time. Netlit always reports that secondary ion alongside the one you asked for. Molar masses are computed from atomic weights rather than carried around as rounded constants.

Register liquid products from their own label

There is no built-in database of commercial products — third-party trademarks stay out of the app. Instead there is a wizard that works backwards from the label on your bottle. Enter a statement like "x mL per y litres raises z mg/L" and from then on that product is dosed in millilitres against your net volume. Dechlorinator works the same way: register the dilution your own bottle specifies.

Calculate, and it is already a record

The log button sits inside the result card. There is no screen to navigate to. Each entry stores a snapshot of the net volume at that moment, the formula version, your inputs and the result.

So when you rescape the tank later and the net volume changes, your old entries do not silently change with it. The detail view shows both: "41.0 L then (44.2 L now)". Water tests can be edited; any entry can be deleted, and a deletion can be undone.

Seven parameters, charted

Log NO₃, PO₄, KH, GH, pH, TDS and temperature, with no cap on the number of entries, and follow the trend in Swift Charts.

How fast nitrate is actually building up

Once two or more measurements exist, Netlit estimates the daily nitrate production rate — excluding any stretch with a water change in the middle — and projects the steady-state concentration your current water-change routine converges to.

When there is not enough data, it does not report "none" or "0 per day". It tells you how many usable stretches it found and what to record next so an estimate becomes possible.

Free and Premium

Netlit Premium is an auto-renewing subscription, billed monthly or yearly; the price for your region is shown on the App Store. Net volume, water changes, dosing and the number of entries are never capped on the free tier. If you cancel, viewing, editing, deleting and backing up your records continues to work.

How your data is handled

Netlit makes no network connections. No account is required and nothing is sent to the developer. There is no analytics SDK and no advertising SDK, so the developer has no way of knowing how the app is used.

If iCloud Backup is enabled on your device, Netlit's data is included in Apple's backup like any other app's. That backup is handled by Apple, not by Netlit.

Exporting a full backup file and restoring from one are free.

What it does not do

• No marine tanks. Ca / KH / Mg balance and CO₂ estimation are out of scope for v1.0.
• No medication dosing.
• No fish species database.
• No presets for commercial products. You register your own from the label.
• No sync between devices. Moving data is done with a backup file.

Please note

The figures this app produces are general calculations, not veterinary advice. What is appropriate depends on your livestock, the tank's history and the accuracy of your test kit. Measure your water yourself before changing it or dosing, and make the final call yourself.