Verdict
Use a note for ideas. Use a structured log for measurements — anything you will want to compare later needs a field, not a sentence.
| Notes app | FishTank Diary | |
|---|---|---|
| Entry friction | Very low | Low (structured fields) |
| Comparable data | Numbers in prose | Typed fields, chartable |
| Reminders | Manual | Scheduled per tank |
| Multiple tanks | One note per tank, if you remember | Built-in separation |
| History quality | Degrades as it grows | Consistent by design |
| Cost | Free | $3.99 once |
The structured-vs-freeform trade-off
Freeform notes are faster to write and impossible to query. “pH 7.2, nitrate 20, changed 30%” is three data points buried in a sentence; the app stores the same information as three fields that can be charted, compared and exported. That difference only matters after a few months — which is exactly when you need the history.
A hybrid that works
Keep the note for observations — behaviour, colour, a plant that melted — and put the numbers in the log. The app has a notes field on each entry for exactly this reason.
