Complete Guide to Reverse Osmosis (RO) Systems for Aquariums

Reverse Osmosis (RO) systems are one of the most reliable ways to produce pure water for aquariums. Whether you keep delicate freshwater shrimp, soft-water plants, or sensitive marine corals, RO ensures you start with a clean slate — free of harmful impurities.

How an RO System Works

RO systems filter water in stages, removing progressively finer impurities until the output is nearly pure H₂O.

1. Sediment Filter (Pre-filter)

• Purpose: Removes large particles such as sand, rust, dirt, and silt.

• Why important: Protects the delicate RO membrane from clogging.

• Lifespan: Typically changed every 6–12 months.

2. Carbon Block Filter

• Purpose: Removes chlorine, chloramines, pesticides, and volatile organic compounds (VOCs).

• Why important: Chlorine/chloramine will damage the RO membrane and harm fish if it passes through.

• Lifespan: Every 6–12 months, depending on water quality.

3. RO Membrane

• Purpose: The heart of the system. Removes 95–99% of dissolved solids (salts, heavy metals, nitrates, phosphates, fluoride, etc.).

• Micron size: Filters down to ~0.0001 microns.

• Lifespan: 2–5 years, depending on water pressure, incoming water quality, and maintenance.

• Wastewater: Produces “reject water” containing concentrated impurities.

4. Deionization (DI) Resin (optional but essential for reef tanks & shrimp keepers)

• Purpose: Polishes water to 0 TDS by removing remaining charged ions (both positive and negative).

• Removes: Silicates, phosphates, nitrates, and any leftover trace minerals.

• Lifespan: Replace once TDS after DI rises above 1–2 ppm.

What is TDS?

TDS (Total Dissolved Solids) measures the concentration of dissolved substances in water (calcium, magnesium, nitrate, phosphate, copper, etc.).

• Tap water TDS: 100–500 ppm (varies by region).

• After RO membrane: 5–50 ppm.

• After DI resin: 0 ppm (ideal for reef and delicate freshwater aquaria).

TDS Meter Placement

A good RO/DI setup uses dual or triple inline TDS meters to monitor system performance.

1. After RO membrane, before DI resin → tells you membrane performance.

2. After DI resin (final output) → ensures you’re producing 0 TDS water.

Other Key Components

1. Pressure Restrictor

• Controls water flow across the membrane.

• Maintains the correct ratio of pure water (product) to wastewater (reject).

• Prevents premature membrane wear.

2. Booster Pump (Pressure Pump)

• Raises incoming water pressure (ideal pressure: 60–80 PSI).

• Low pressure (<40 PSI) reduces RO efficiency and increases waste.

• Essential in areas with weak mains pressure.

Maintenance & Replacement Schedule