Aquarium TDS FAQ: Targets per Tank Type and Meter

TDS — total dissolved solids — measures everything dissolved in your water in parts per million. Singapore PUB tap reads 80-110 ppm out of the pipe; a community tropical tank typically holds 150-300 ppm depending on stocking and dosing. Crystal shrimp need precise 100-130 TDS on RODI plus remineraliser. This aquarium tds faq from Gensou Aquascaping at 5 Everton Park covers targets, meters and trends, and this guide answers the 10 questions Singapore aquarists ask most about TDS.

What does TDS actually measure?

TDS measures total ionic content — minerals, salts, fertilisers, and dissolved organics — through electrical conductivity. It does not distinguish between beneficial calcium and harmful nitrate; a tank can have low TDS and high nitrate or vice versa. TDS is a useful trend indicator paired with specific tests for individual parameters.

What TDS should I target?

Community tropical: 150-300 ppm. Cherry shrimp: 200-300 ppm. Crystal shrimp: 100-130 ppm. Discus: 80-150 ppm. Tanganyikan cichlids: 350-500 ppm. Marine reef: 35,000-37,000 ppm (specific gravity 1.024-1.026). Within these ranges, stability matters more than exact value — drift under 30 ppm per week is normal.

How accurate are TDS pens?

HM Digital TDS-3 at SGD 18-25 reads within 2 per cent and is the hobby standard. ATC Aquatech pens at SGD 25-40 are similar accuracy. Calibrate monthly with a 342 ppm or 1413 µS/cm calibration solution. Tropical humidity drifts pen accuracy fast — check against a known-good source if readings seem off. Pick up replacement pens from aquarium tools.

Why does my TDS climb over time?

Evaporation concentrates dissolved solids. Singapore tanks lose 1-2 litres per 100L per day to evaporation. Top-up with RODI water — never with tap, which adds fresh minerals and accelerates the climb. Fertiliser and food residue also raise TDS. Weekly water changes reset the level back toward source water.

What TDS does Singapore PUB tap have?

80-110 ppm year-round, with monthly variation of 10-20 ppm. NEWater-blended supplies sit lower; reservoir-fed estates higher. Test on the day of a water change for accurate matching of change water to tank water — TDS swings of more than 30 ppm stress shrimp.

Should TDS rise or fall between water changes?

Rise, slightly. Fish waste and fertilisers add ions; evaporation concentrates everything. A typical planted community tank rises 20-50 ppm per week. If TDS falls, you are likely topping up with RODI faster than ions accumulate, which is acceptable but means lighter water changes.

Do I need a TDS meter for non-shrimp tanks?

Useful but not essential. For a basic community tank with PUB tap and weekly water changes, TDS rarely matters. For planted high-tech, breeding projects, or shrimp keeping, a meter is mandatory. The SGD 18-25 entry-level meters justify themselves within months.

How do I lower TDS quickly?

Larger water changes with low-TDS source water. RODI water has 0-5 ppm — a 50 per cent change with RODI cuts tank TDS in half. Plain tap at 80-110 ppm reduces tank TDS slowly because the tap baseline is itself elevated. Shrimp emergencies need RODI changes within hours.

What raises TDS unexpectedly?

Aquasoil leaching during break-in (weeks 1-3 add 50-150 ppm), heavy fertiliser dosing especially Estimative Index regimes, salt added to “treat” stressed fish, and crushed coral or aragonite slowly dissolving. Also: leftover food and corpses break down into ionic mass. Browse water care for low-TDS dosing alternatives.

What if RODI water reads above 0 ppm?

Standard four-stage RODI units output 1-10 ppm depending on membrane condition. Above 15 ppm indicates membrane wear or saturated DI resin. Replace the DI resin first; if still high, replace the RO membrane. Crystal shrimp keepers need TDS under 5 ppm out of the unit before remineralisation.

Related Reading

• Aquarium GH and KH FAQ
• Aquarium pH FAQ
• Tap Water Aquarium FAQ
• Water Change FAQ
• Cherry Shrimp FAQ