How to Remineralise RO Water for Aquariums: Shrimp and Fish
Reverse osmosis strips tap water down to near-zero mineral content — perfect as a blank canvas, but lethal to aquatic life if used untreated. This remineralise RO water aquarium guide from Gensou Aquascaping at 5 Everton Park, Singapore walks you through why remineralisation matters, which products to use, and how to hit precise targets for both shrimp and fish. With over 20 years of hands-on experience, we have fine-tuned this process across hundreds of setups.
Why RO Water Needs Minerals
Pure RO water has a TDS near zero, no general hardness (GH), and virtually no buffering capacity (KH). Fish and invertebrates rely on dissolved calcium and magnesium for shell formation, osmoregulation, and nerve function. Water without KH has no pH buffer — a tiny amount of acid from biological processes can crash the pH overnight.
Singapore’s PUB tap water is already soft (GH 2–4 dGH), so some hobbyists question the need for RO at all. The main reasons to use it here are consistency — tap parameters shift slightly between seasons — and the removal of chloramine, heavy metals, and silicates that fuel diatom blooms.
Choosing the Right Remineraliser
Products fall into two broad categories. GH-only remineralisers, such as SaltyShrimp GH+, add calcium and magnesium without raising KH. These are designed for caridina shrimp species like crystal reds and Taiwan bees, which thrive in soft, acidic conditions buffered by active substrate rather than carbonate hardness.
GH/KH remineralisers, such as SaltyShrimp GH/KH+, add both general hardness and carbonate alkalinity. Use these for neocaridina shrimp, community fish, and planted tanks running inert substrate. They provide the pH stability that most tropical fish need. A 200 g tub costs around $18–$25 on Shopee and lasts months for a typical nano setup.
Target Parameters for Common Livestock
Caridina shrimp (crystal red, Taiwan bee, shadow panda) prefer GH 4–6, KH 0–1, TDS 100–150, and pH 5.8–6.5 buffered by active soil. Neocaridina (cherry, blue dream, yellow) are more forgiving: GH 6–8, KH 2–4, TDS 150–250, and pH 6.8–7.5.
Most community fish — tetras, rasboras, corydoras — do well in the neocaridina range. Livebearers like guppies and endlers appreciate even harder water: GH 8–12, KH 4–8. Always research the specific species you keep rather than applying a single recipe to every tank.
How to Mix Correctly
Fill a clean bucket or storage container with RO water. Add the remineraliser gradually, stirring as you go, and measure TDS with a handheld meter after each addition. TDS pens are accurate enough for this purpose and cost under $15 locally. Let the solution stabilise for 10–15 minutes before taking a final reading.
For SaltyShrimp GH+, roughly one scoop (the included measuring spoon) per 10 litres raises TDS by about 30–40 ppm. Start conservatively — you can always add more, but removing excess minerals requires diluting with more RO water. Record your recipe once dialled in so every batch is identical.
Batch Preparation and Storage
Preparing water in advance saves time on water change day. A 60-litre food-grade bin with a lid and a small airstone keeps remineralised water ready for use. Aeration prevents stagnation and helps degas any residual CO2 from the RO membrane process.
Store premixed water no longer than three to four days. Beyond that, bacterial biofilms can develop even in mineralised water. Label each container with the TDS and date mixed — a habit that prevents accidental parameter swings, especially if you manage multiple tanks with different requirements.
Common Mistakes to Avoid
Using a GH-only product in an inert-substrate tank without any KH buffer is a recipe for pH instability. Conversely, adding GH/KH+ to an active-soil caridina tank fights the substrate’s acidifying function and exhausts it faster. Match the remineraliser type to your substrate and livestock combination.
Eyeballing powder amounts instead of measuring leads to inconsistency between batches. Even small TDS variations of 30–40 ppm between water changes can trigger moulting issues in shrimp. Invest in a TDS pen and a small digital scale — precision costs very little but protects expensive livestock.
Integrating RO Into Your Routine
Most hobbyists in Singapore run a compact RO unit under the kitchen sink, feeding into a 20–40 litre storage tank. Units producing 50–100 gallons per day cost $80–$150 on Lazada and fit comfortably in an HDB flat. Replace sediment and carbon pre-filters every six months, and the RO membrane annually, to maintain output quality.
Knowing how to remineralise RO water for your aquarium gives you repeatable, pristine water chemistry — arguably the single biggest factor in long-term shrimp survival and vibrant fish health. At Gensou Aquascaping, it is a cornerstone of every high-grade setup we build.
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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
