Aquarium RODI System Anatomy Glossary Guide: Sediment Carbon RO DI
Aquarium RODI system anatomy in fifty words: a reverse-osmosis deionisation system removes 95-99 per cent of dissolved solids from tap water through a five-stage cartridge sequence — 5-micron sediment, 1-micron sediment, carbon block, semi-permeable RO membrane and mixed-bed DI resin. The output is near-pure water at 0 TDS, suitable for reef tanks, shrimp keepers and discus breeders. Knowing the aquarium RODI system anatomy stage-by-stage helps you replace cartridges on schedule, which this Gensou Aquascaping guide from 5 Everton Park breaks down with rejection and waste-ratio numbers.
Stage One: 5-Micron Sediment Pre-Filter
Tap water enters the system through a 5-micron melt-blown polypropylene sediment cartridge. This stage traps sand, rust, silt and large particulates that would otherwise score the RO membrane. Singapore PUB tap is generally clean, so 5-micron cartridges last 6-8 months in domestic use. Replace when you see visible discolouration or a 20 per cent flow drop.
Stage Two: 1-Micron Sediment Polish
The second sediment cartridge traps finer suspended particulates down to 1 micron. Some systems combine stages 1 and 2 into a single cartridge; quality 5-stage systems separate them for membrane longevity. Sediment filters cost SGD 8-15 each and represent the cheapest stage to replace. Skipping replacements shortens membrane life dramatically.
Stage Three: Granular Activated Carbon Block
The carbon block removes chlorine, chloramine and dissolved organics. This is the most critical pre-stage because chlorine destroys thin-film composite RO membranes within hours of exposure. Standard coconut-shell carbon blocks handle chlorine; chloramine-rated blocks (catalytic carbon or specialised media) are essential in Singapore where PUB uses chloramine year-round. Browse the filter cartridge selection for chloramine-spec replacements.
Stage Four: The RO Membrane
The semi-permeable thin-film composite (TFC) membrane is the heart of the system. Tap water at 60-80 psi forces through a polymer film with pores around 0.0001 micron, blocking dissolved salts, heavy metals and most organics. Membranes are rated by daily output: 50 GPD, 75 GPD, 100 GPD or 150 GPD. The 75 GPD membrane is the residential sweet spot. Rejection rate sits at 95-99 per cent depending on feed pressure and TDS.
Waste-to-Product Ratio
RO systems produce one part purified water for every 3-4 parts waste water that flushes concentrated dissolved solids down the drain. A 75 GPD membrane producing 280 litres per day discharges 1100 litres of waste — significant in HDB water bills. Permeate pumps and waste-water capture for laundry use cut bills meaningfully. Singapore water tariffs make RODI more expensive to run than in temperate climates.
Stage Five: Mixed-Bed DI Resin
The final stage polishes RO permeate from 5-15 TDS down to 0 TDS using mixed-bed deionisation resin — equal parts cation (H+ form) and anion (OH- form) exchange beads. The resin captures the last residual ions through ionic substitution, producing water indistinguishable from laboratory-grade ultrapure. DI resin colour-changing variants (tea-coloured when exhausted) signal replacement timing — typically every 2000-4000 litres of throughput.
The TDS Meter Verification Step
A handheld TDS meter (HM Digital TDS-3 at SGD 25-35) is essential for any RODI user. Measure feed-water TDS, post-RO TDS and post-DI TDS regularly. Singapore PUB tap runs 60-120 ppm; post-RO should drop to 5-15 ppm; post-DI must read 0 ppm. Rising post-DI numbers mean it is time to swap resin.
Booster Pump and Flow Considerations
Singapore HDB water pressure averages 2-3 bar (29-44 psi) — borderline low for RO membranes which need 50+ psi. A booster pump (SGD 80-150) lifts feed pressure to 80 psi and increases membrane efficiency by 30-50 per cent. Without one, 75 GPD membranes deliver closer to 40 GPD.
Singapore Sourcing and Costs
Complete 5-stage RODI systems from Spectrapure, Bulk Reef Supply and AquaPro retail at SGD 280-650 in Singapore reef shops. Replacement cartridge sets run SGD 60-110 annually for an average reef setup. The marine aquarium section at Gensou stocks RODI components and replacement membranes.
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