Test strips are not inaccurate but prone to user error. Brands to avoid: Tetra and API. The latter, I am almost positive, are bad on purpose so people buy the
liquid test kit out of frustration. I myself use JBL (with and without the reader app, as I have some problems with distinguishing certain colour shades.) and I would also recommend Sera. Both are higher quality than Tetra and API and are quite reliable (provided the general handling is correct).
What to make sure when using teststrips:
- The water on the test fields must not mix. Any mix between two test fields and you can forget those two readings. It's best to just hold it against a paper towel right after dipping into the water. Especially NO3/NO2 and
KH/
pH are prone to that problem and show the strongest reactions when mixed.
- Secondly they are only accurate within a certain scale. Many strips have only a scale with big steps and whole ranges per step.
- Only the readings exactly after 60sec (+10) are accurate. If you wait too long or read too early the results are off.
- They are sensitive to longer open times of the package. Leaving the tube open for more than 5-10min may ruin the whole batch depending on your air humidity. Also the older the less reliable.
They are designed for quick and/or general tests, not accuracy. It's for checking if a reading is above/below a certain level, if chlorine/NO2 are present or if the water is rather hard or soft. For most fishkeepers (new and advanced alike) that don't do setups that require high accuracy this is enough. For high-tech planted tanks with finetuned fertilizers, advanced shrimpkeeping and saltwater setups they are definitely only good for quick checks.
E.g. for my blackwater tank I only use them to quick check the overall NO3-Level. NO2 doesn't show up anyway, GH/KH are below general detection level and pH is below the range. Chlorine is usually not in the tap, only when the public system has been compromised they flush with chlorine for a day or two. In a bad year this happens maybe twice. And the RO unit removes it anyway.
So I test pH with a drip test and I use a
TDS/EC meter aswell.