TDS creeps up quietly in a pond that never gets water changes, even when every other test reads normal. It measures the combined concentration of dissolved minerals, salts, and organic matter in the water.
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Why It Rises Over Time
Evaporation removes pure water but leaves dissolved solids behind, so TDS concentrates over time unless diluted by fresh water.
When to Actually Worry
A slowly rising TDS isn’t usually an emergency, but a sudden jump can signal a problem, and consistently high TDS makes fish more vulnerable to stress and disease over time.
