1
Source Water
Measure tap or feed water first to establish incoming TDS.
Digital TDS-3 Meter for Water Testing — 0–9990 ppm, ±2% Accuracy, Auto-Off — SKU TDSMETER
$8.00
TDS 3 Meter. SKU# TDS3
- Description
- Additional information
- Reviews (1)
Description
Water testing & RO performance monitoring
Quickly check dissolved-solids levels and track RO membrane performance
The TDS-3 digital meter provides a fast way to measure Total Dissolved Solids in drinking water, RO water, aquariums, hydroponic systems, and other water-treatment applications. It is especially useful for comparing source water with purified RO water and for watching changes in membrane performance over time.
0–9990 ppmMeasurement range
±2%Listed accuracy
10 minAuto-off
SKU TDSMETERMyAquaFilter SKU
Key benefits
A simple tool for understanding RO water quality trends
Measure Dissolved SolidsProvides a ppm reading that reflects dissolved ionic content.
Check RO PerformanceCompare source water and RO permeate to monitor membrane rejection trends.
Watch DI ExhaustionUseful for checking when deionization media is no longer producing ultra-low-TDS water.
Auto-OffPowers down after about 10 minutes of inactivity.
How to use with RO
Take readings at the correct points in the system
2
RO Permeate
Measure purified water immediately after the RO membrane and before remineralization, alkaline, KDF, calcite, or other post-filters.
3
Compare Trends
Use repeat readings over time to watch membrane rejection and filtration performance.
Specifications
Product details
| Product type | Digital TDS water-quality meter |
|---|---|
| Measurement | Total Dissolved Solids (TDS) |
| Range | 0–9990 ppm |
| Resolution | 1 ppm from 0–999 ppm; 1000–9990 ppm displayed using ×10 multiplier |
| Listed accuracy | ±2% |
| Auto-off | After approximately 10 minutes |
| Power | 2 × 1.5V button-cell batteries |
| Batteries included | Yes |
| Package includes | 1 TDS meter + instructions |
| Listed shipping dimensions | 4 × 2 × 1 in |
| Listed shipping weight | 6 oz |
| SKU | TDSMETER |
For more accurate RO readings
- ✓Use the RO system normally for about 5–7 days after installing a new system or replacing filters before evaluating TDS performance
- ✓Fresh carbon filters can temporarily add a few ppm because of normal carbon fines and initial flushing
- ✓Test directly after the RO membrane and before remineralization or alkaline filters when evaluating membrane rejection
- ✓Rinse the probe with clean water between samples
Where to take a TDS sample
Measure at the correct filtration stage for meaningful RO readings
RO
Countertop RO Systems
For the most useful membrane-performance reading, take the water sample immediately after the RO membrane stage, before any carbon polishing, alkaline, or remineralization filter.
US
Under-Sink RO Systems
Use the same approach: sample the purified water directly after the RO membrane whenever possible. This gives the clearest indication of membrane rejection.
DI
RO + DI / Ion Exchange
For ultra-pure systems, you can test both after the RO membrane and after the final DI or ion-exchange stage. The RO reading shows membrane performance; the final-stage reading shows the polishing performance of the DI media.
MIN
RO + Remineralization / Alkaline
Take the sample before the mineralization stage—preferably directly after the RO membrane. Remineralization and alkaline media intentionally add mineral ions back to the water, so the final TDS will be higher by design.
Why TDS may rise after post-filtration
Higher final TDS does not necessarily mean the RO membrane is performing poorly
Carbon Filters
New carbon filters can temporarily add a few ppm to the reading because of normal carbon fines and fresh-media flushing.
Remineralization Filters
Mineral and alkaline post-filters intentionally add dissolved calcium, magnesium, and other mineral ions. Depending on the media and water chemistry, final TDS may increase by roughly 10–60 ppm or more.
DI / Ion Exchange
DI media works in the opposite direction: it removes remaining dissolved ions after RO and can bring the final reading down toward ultra-low TDS when the resin is fresh.
Timing matters
Do not evaluate a new RO system or fresh filter set immediately after installation
For a more representative reading, use the RO system normally for approximately 5–7 days after installing a new system or replacing filters before evaluating TDS performance. Fresh carbon media, new mineral media, initial flushing, and stabilization of the RO membrane can temporarily affect early readings.
Good to know
TDS is useful for trends — not a complete contaminant test
!
TDS does not identify contaminantsIt estimates dissolved ionic content but does not tell you which minerals, salts, or contaminants are present.
!
Low TDS does not certify potabilityThe meter does not test bacteria, viruses, pesticides, PFAS, VOCs, or individual metals.
For RO membrane evaluation, compare source-water TDS with RO permeate before any mineral, alkaline, calcite, KDF, or other post-treatment stage. Mineral post-filters can intentionally raise final TDS even when the RO membrane is performing normally.
Need help interpreting a TDS reading?Send source-water and RO-permeate readings plus your system model.
Additional information
| Weight | 6 oz |
|---|---|
| Dimensions | 4 × 2 × 1 in |
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