RODI (Reverse Osmosis + Deionization) is a multi-stage water filtration process that produces ultra-pure water (0 TDS) for reef + planted aquarium use. Tap water contains chloramines, phosphates, copper, and other contaminants harmful to aquatic life; RODI strips them.
Practical use in aquariums
A typical 4-stage RODI unit: sediment filter → carbon block → RO membrane → DI resin. Test output with a TDS meter: 0 ppm = clean. RO membranes last 2-3 years; DI resin lasts 6-12 months depending on source water quality.
How RODI fits the bigger picture
Understanding RODI matters because it's connected to broader husbandry decisions: equipment selection compounds: skimper + return + dosing all need to match each other and the tank size.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.