The values of TDS (Total Dissolved Solids) water quality tester and the water quality rating standards are as follows:
TDS Value Range and Water Quality Rating
| TDS Value Range (ppm) | Water Quality Type and Rating |
|---|---|
| 0 – 50 | Pure water, very pure water quality, suitable for drinking. |
| 50 – 100 | Mineral water or high-quality drinking water, good water quality, contains certain minerals. |
| 100 – 300 | Tap water, average water quality, suitable for daily drinking. |
| 300 – 600 | Poor water quality, may contain more impurities, bad taste. |
| 600 – 1000 | Poor water quality, may contain more soluble salts and impurities. |
| >1000 | Very poor water quality, not suitable for drinking. |
TDS Value Standards for Different Types of Water
- Pure Water: TDS value should be below 50ppm.
- Mineral Water: TDS value is usually between 100ppm and 200ppm.
- Tap Water: Qualified TDS value should be below 300ppm.
Notes
- The TDS value can only reflect the content of total dissolved solids in the water and does not fully represent the safety of water quality.
- The measurement results of the water quality tester may be affected by factors such as water temperature. It is recommended to conduct the measurement at around 25℃.
What TDS can and cannot tell you
TDS measures dissolved solids, but it does not identify what those solids are. A high reading can come from minerals, salts, fertilizers, or accumulated waste. A low reading can still be unsafe if ammonia or nitrite is present. Treat TDS as a trend tool, not a complete water-quality test.
| Pattern | Possible meaning | Next check |
|---|---|---|
| TDS rises every week | Minerals, fertilizer, food waste, or evaporation concentration | Nitrate, GH/KH, water-change routine |
| TDS suddenly jumps | New additive, rock, substrate, salt, or dosing error | Recent changes and livestock behavior |
| TDS very low | Soft or purified water | GH/KH stability and species needs |
| TDS stable but fish stressed | Problem may not be dissolved solids | Ammonia, nitrite, oxygen, temperature |
For most community aquariums, consistency matters more than chasing a universal TDS number.
Decision boundary
Use this page as a practical starting point, then verify the result against the aquarium in front of you. Tank size, filter maturity, temperature stability, livestock count, feeding amount, and water-change rhythm can all change the right answer. A number or rule that works in a mature 20 gallon tank may fail in a newly set up 5 gallon tank.
Common misread
The most common mistake is treating a single care-sheet fact as permission to skip observation. If fish hide, gasp, clamp fins, refuse food, lose color, or show torn fins, pause the plan and test water before adding livestock, changing products, or increasing feeding. Stable behavior and stable water matter together.
Next useful check
- Confirm ammonia and nitrite are 0 ppm before interpreting most behavior problems.
- Compare nitrate before and after the normal water-change interval.
- Check whether the filter flow, decor, and tank mates match the species rather than the tank label.
- Make one change at a time so the cause of improvement or decline stays visible.
Practical follow-through
The safest way to apply this advice is to write down the current tank state before changing anything: tank volume, filter type, livestock count, latest water tests, feeding amount, and the last maintenance date. That record turns a vague fishkeeping question into a sequence of checks that can be repeated.
After making a change, wait long enough to observe the result unless fish are in immediate distress. Many aquarium problems become harder to diagnose when food, chemicals, filter media, lighting, and stocking all change on the same day. A measured single change gives you a clearer answer.
When to pause
Pause additions or upgrades if ammonia or nitrite is detectable, if fish are gasping or hiding, if a new fish has not completed observation, or if the tank has just gone through a major cleaning. In those cases, the next useful action is usually testing, stabilization, and observation rather than another purchase.