Aquarium TDS Explained: What It Means and When It Matters
TDS meters are cheap, instant, and everywhere in the aquarium hobby — but the number on the screen tells you far less than many hobbyists believe. Total dissolved solids is a useful tool when you understand its limitations and context. This aquarium TDS explained guide from Gensou Aquascaping at 5 Everton Park, Singapore, clarifies what TDS actually measures, when it matters, and when you can safely ignore it. With over 20 years of hands-on experience, we have seen too many keepers chase a TDS number without understanding what drives it.
What TDS Actually Measures
A TDS meter measures the electrical conductivity of water and converts it to an approximate parts-per-million figure. It detects anything that conducts electricity when dissolved — calcium, magnesium, sodium, potassium, nitrate, phosphate, fertiliser salts, tannins, and more. Crucially, it cannot distinguish between these substances. A reading of 200 ppm might mean healthy mineral content or it might mean accumulated waste. Context is everything.
TDS Ranges for Common Setups
Singapore’s PUB tap water typically reads 60–90 ppm TDS — relatively low by global standards. For neocaridina shrimp, a range of 150–250 ppm supports healthy moulting and breeding. Caridina species like crystal red shrimp prefer lower values of 100–150 ppm, achieved by using remineralised RO water. Most tropical community fish are unfazed by TDS anywhere from 100 to 400 ppm, making it a less critical parameter for fish-only setups.
Planted tanks with liquid fertiliser dosing often show elevated TDS — this is expected and not harmful. A spike of 50–100 ppm after a fertiliser dose does not mean your water quality has declined.
When TDS Matters Most
Shrimp keeping is where TDS monitoring earns its keep. Caridina shrimp are sensitive to mineral fluctuations, and a TDS meter provides a quick daily check for consistency. If your target is 130 ppm and you wake up to 200 ppm, something has changed — evaporation concentrating minerals, a forgotten fertiliser dose, or decaying organic matter. Investigating that discrepancy before it harms your colony is where a TDS meter proves its value.
RO water preparation also benefits from TDS monitoring. A fresh RO membrane should produce water at 0–10 ppm; if the output reads 30+ ppm, the membrane needs replacing. This simple check saves you from unknowingly introducing impure water to a sensitive shrimp tank.
When TDS Is Misleading
Hobbyists sometimes panic when TDS rises after adding driftwood (tannin release), dosing KH buffer, or using mineral supplements — all of which raise TDS without reducing water quality. Conversely, a tank with low TDS but high ammonia reads “clean” on a TDS meter while being lethal. Never use TDS as a substitute for testing ammonia, nitrite, nitrate, pH, KH, and GH individually. It supplements those tests; it does not replace them.
Choosing a TDS Meter
Basic pen-style TDS meters cost $5–$15 on Shopee and Lazada and are accurate enough for aquarium use. Calibrate with a standard solution (usually included) every few months. Store the meter dry with the cap on to protect the electrodes. Higher-end models with temperature compensation improve accuracy slightly but are unnecessary for most hobbyists. The key is consistency — use the same meter at the same time of day for comparable readings.
Managing TDS Through Water Changes
Regular water changes are the simplest way to keep TDS in check. In a shrimp tank targeting 150 ppm, weekly 10–15 % changes with remineralised RO water at the same TDS maintain stability. For fish tanks on tap water, standard 20–30 % weekly changes prevent TDS from climbing as waste accumulates. If TDS creeps up faster than your water change schedule controls, investigate overfeeding, excess fertiliser dosing, or insufficient filtration as possible causes.
TDS and Singapore’s Water Supply
PUB water quality is remarkably consistent, but minor seasonal fluctuations do occur. Heavy monsoon rain can dilute reservoir water slightly, lowering TDS by 10–20 ppm. Dry spells may raise it marginally. For most fish keepers, this variation is irrelevant. For caridina breeders aiming at tight TDS windows, testing source water before each batch of remineralised water ensures precision. This aquarium TDS explained guide principle — measure, understand, then act — applies to every parameter, not just TDS.
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Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
