Municipal tap water in the US is treated for human consumption, not aquatic life. It contains chlorine, chloramine, copper from old pipes, phosphates from anti-corrosion treatments, and trace amounts of pesticides, pharmaceuticals, and heavy metals. None of these are at levels that hurt humans. All of them are at levels that hurt sensitive shrimp, soft coral, and SPS coral. Caridina shrimp in particular die in tap water within days because the dissolved-mineral profile is wildly different from their native blackwater habitat.
Reverse osmosis pushes water through a semi-permeable membrane that strips out 95-98% of dissolved solids, including most of the contaminants above. Deionization is a polishing stage with two ion-exchange resins (cation and anion) that remove the remaining 2-5%. The output is essentially pure water with a TDS reading of zero. A four-stage RO/DI unit with a sediment pre-filter, a carbon block, an RO membrane, and a DI canister is the standard setup for both reef and shrimp keeping. Six-stage units add a second carbon block and a second DI canister for redundancy on chloramine-treated water sources.
Aim for 0 ppm TDS (total dissolved solids) at the output. A reading above 2-3 ppm means the DI resin is exhausted and needs replacing. The membrane itself does not need replacing as often as people think - good membranes last 2-3 years on properly pre-filtered water. The DI resin is the consumable that runs out fastest because it carries the load when membrane efficiency drops.
Pure RO/DI water is too clean for shrimp - they need specific calcium, magnesium, and KH levels to molt successfully. Shrimp keepers add remineralizers like Salty Shrimp GH+, GH/KH+, or Bee Shrimp Mineral GH+ to bring TDS back up to the right target (usually 100-180 ppm depending on Caridina vs Neocaridina). The mineral profile from these products is matched to shrimp physiology, not to whatever your tap water contains.
BRS (Bulk Reef Supply) and AquaFX produce the most popular hobbyist units. BRS units are well-built and include excellent documentation; AquaFX runs slightly cheaper. SpectraPure is the upgrade tier - higher waste-water ratio efficiency and longer membrane life. For shrimp-only setups a small BRS 4-stage 75 GPD unit is plenty; for reef tanks running 100+ gallons of water changes a month, step up to a 100-150 GPD unit with a second carbon block.
Running the unit at low pressure (below 50 psi) kills RO membrane efficiency. So does cold incoming water - membranes are rated at 77F and produce dramatically less water at 60F. Never let DI resin sit dry between uses; it permanently loses capacity. And replace your sediment and carbon pre-filters every 6 months even if the manufacturer says 12 - cheap pre-filters extend the life of expensive membranes by orders of magnitude.
Recommendations on this page cross-checked against the following authoritative references and our internal vendor + breeder database.
Answers to the questions experienced keepers ask after the basic care guide.
Drip acclimation over 60 to 90 minutes is the safest approach for RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics. Match temperature first (15 minute float), then drip 2 to 3 drops per second from the display sump until the bag volume has tripled. Test salinity (or freshwater hardness) at the end - if it is within 0.001 SG (or 2 dGH) of the display, transfer the specimen with a net rather than pouring shipping water in.
Aim for biological + mechanical + chemical staging. Canister or sump-driven filtration sized for 5x to 8x display turnover per hour, mechanical floss replaced weekly, and carbon or GAC swapped every 4 to 6 weeks. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics responds well to stable nitrate (under 20 ppm) more than to any specific filter brand - stability beats peak performance.
For saltwater specimens, yes - a properly-sized skimmer rated for 1.5x to 2x display volume keeps dissolved organics low and reduces nuisance-algae triggers. Freshwater specimens do not need skimmers; a well-stocked plant grow-out + canister with chemical media achieves the same end. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics kept without adequate organic export tends to show stress within 90 days.
Compatibility with planted tanks depends on the species behavior + water chemistry overlap. Plant-safe specimens leave foliage alone; some pick at soft-tissue plants like vallisneria or anubias. Check the species page profile + the planted-tank compatibility note before stocking RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics in a high-tech CO2-injected setup with valuable cultivars.
For freshwater specimens with no plant requirements, a basic LED at 30 to 50 PAR at substrate is sufficient and reduces algae. For saltwater + reef specimens, target 100 to 250 PAR depending on photo-tolerance, with a sunrise/sunset ramp + a 8 to 10 hour photoperiod. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics tolerates a wider lighting band than most keepers expect; consistency matters more than peak intensity.
Most aquarium species evolved in moderate flow with localized turbulence rather than uniform high flow. Aim for 20x to 40x display turnover for reef specimens, 4x to 6x for community freshwater. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics shows stress fins (clamped, frayed) when flow is mismatched - dial back if you see this within 14 days of introduction.
Sustained drift above +/- 2 F from target is the threshold most keepers miss. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics tolerates day-night swings of 1 to 2 F without issue but a 4 F shift over 2 hours triggers ich + bacterial bloom risk. Use a controller-driven heater (not the built-in dial) and a backup thermometer at the opposite end of the tank.
For freshwater fish: ich, columnaris, and fin rot are the top three; quarantine + UV sterilizer prevents the majority. For marine fish: ich (Cryptocaryon), velvet (Amyloodinium), and bacterial infections; tank-transfer method or copper QT during the 30-day acclimation cycle prevents nearly all outbreaks. For inverts + corals: tissue necrosis, parasitic isopods, and protozoan blooms.
Captive breeding success varies enormously by species - some breed readily in community tanks (livebearers, cherry shrimp, clownfish) while others have never been captive-bred (most reef fish + most marine inverts). Check the species-specific care guide for the breeding-method note + larval-rearing protocol. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics kept in pairs or small groups often spawns even without intent if conditions are right.
Avoid same-species rivals (especially male-male pairings for territorial species), known fin-nippers (tiger barbs, certain pufferfish), and anything that out-competes for food or out-grows the tank. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics also struggles with hyper-aggressive cichlids in freshwater and damselfish in saltwater - both will hold territory at the expense of every other tankmate.
Most ornamental specimens accept cleaner shrimp + cleaner gobies; cleaner wrasses (Labroides) often die in captivity and are not recommended. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics kept with cleaner pairs typically benefits from parasite control + stress reduction, but verify the cleaner does not get eaten by checking the species size + temperament chart.
Captive lifespan tracks closely to wild lifespan when water chemistry, diet, and tankmate stress are managed. Most aquarium fish live 5 to 12 years; long-lived species (large cichlids, pufferfish, some tangs) reach 15+ years. RO/DI water: why tap water kills shrimp and how to set up a unit - Fast Aquatics kept in a stable, properly-sized system should live within 80% to 100% of the species lifespan ceiling - early death usually traces back to chronic-stress causes (parameters, tankmates, diet) rather than disease.