The short answer
On RO or distilled water in a planted tank, Seachem Equilibrium; for discus, bettas or livebearers, Continuum Reconstitute RO; to make RO/DI water for a small tank, Aquatic Life RO Buddie 4-Stage.
Our verdict
Our Top Picks at a Glance
Culligan, which sells water treatment, says “most freshwater aquariums can safely use treated tap water, while sensitive freshwater and saltwater tanks often benefit from reverse osmosis (RO) water with added minerals” (Culligan). The US EPA says chlorine and monochloramine “must be neutralized or removed if used in aquariums” (EPA): see our water conditioner guide.
This guide covers the RO route: three RO/DI units, and five remineralizers for RO, DI or distilled water. More in water care and testing.
Water finder
Find the water gear for your tank
Pick your tank and what you want to spend. Tiers are by product price: the remineralizers are all entry level, and the RO/DI units are mid-range or premium. The suggestion is our editorial starting point, drawn from the eight products below, not a test result.
Tiers are relative to the products in this guide; live prices are in the comparison table below.
Compare the picks
Compare the 8 picks
Every row is the size we link; figures are the makers’ own.
Seachem EquilibriumPlanted-tank GH powderPlanted tanks on RO waterGH powder600 g$20.79 Prime
Evidence: owner reports, no independent test
Seachem ReplenishLiquid GH for unplanted tanksUnplanted, communityGH liquid500 mL$11.00 Prime
Evidence: owner reports, no independent test
Brightwell Remineraliz-PPowder for RO, DI or distilledPlanted, distilled waterGH and TDS powder250 g$15.90 Prime
Evidence: owner reports, no independent test
Continuum Reconstitute RODose set by fish typeDiscus, bettas, livebearersGH and KH liquid500 mL$14.37 Prime
Evidence: maker specs only, no independent test
Brightwell NeoTiger KH+/GH+Neocaridina shrimp mineralsShrimp, soft waterGH and KH liquid250 mL$11.32 Prime
Evidence: owner reports, no independent test
Aquatic Life RO BuddieCompact entry RO/DI unitSmall tanks, freshwaterRO/DI unit50 GPD$69.99
Evidence: owner reports, no independent test
LiquaGen 5-StagePortable reef-style RO/DIReef, saltwaterRO/DI unit75 GPD$159.99
Evidence: maker specs only, no independent test
iSpring RCC1DHigh-output tankless RO/DILarge tanks, reefRO/DI unit150 GPD$190.31 Prime
Evidence: maker specs only, no independent test
How We Chose the Water Gear
How this guide was built
built from manufacturer documentation, the live Amazon listings and owner reports; we have not tested these products ourselves.
What we compared
- Parameters covered or contaminants removed: what each product raises or removes, per its maker.
- Accuracy against a reference: not applicable; these are not test kits, and the figures are the makers’ own.
- Cost per gallon treated: not calculated; products are compared by relative product price only.
- Ease of use: from the makers’ directions.
- Value: the relative price tier ($ entry level to $$$ premium) set against the criteria above. All eight were in stock on 2026-11-02: six sold by Amazon.com, two by their makers’ storefronts.
Sources, and what owners say
Sources, and what owners say
The ranking articles come from water-treatment sellers (Culligan, Long’s EcoWater, Frizzlife); in the results we read we found no independent test of these products. In the r/Aquariums thread that ranks first, the top reply is “Regular tap water, dechlorinated”; the second-highest says “Purified water is better” than distilled.
Detailed Reviews: The 8 Picks for Making Tank Water
Seachem Equilibrium, Planted-tank GH powder
600 g · 16 g per 20 gal for 3 dGH
Planted-tank keepers on RO or DI water.
$20.79 from AmazonAs of Nov 2, 17:35 UTCVerdict
GH powder with no sodium or chloride, per Seachem.
Evidence: No independent test; owner reports. r/PlantedTank owner: Equilibrium, size not stated.
Seachem designed Equilibrium for “the planted aquarium”, doses it for “DI or RO water”, and says not to use it when replacing evaporated water; premixed, its haze “should clear within 15–30 minutes”. One r/PlantedTank owner who pairs it with Seachem Neutral Regulator says that “works great for me”, but that Equilibrium “can take kind of a while to dissolve fully”.
Specs (linked: 600 g)
- Dose: 16 g per 20 US gal for +3 dGH (Seachem)
Pros
- No sodium or chloride, which Seachem says can harm a planted tank at elevated levels
Cons
- Raises GH; Seachem recommends a separate buffer for KH
Seachem Replenish, Liquid GH for unplanted tanks
500 mL · 5 mL per 10 gal for 2.8 dGH
Fish-only community tanks on RO or DI water.
$11.00 from AmazonAs of Nov 2, 17:35 UTCVerdict
Liquid GH that Seachem recommends for tanks without live plants.
Evidence: No independent test; owner reports. r/axolotls owner: Replenish, size not stated.
Seachem says Replenish restores minerals “removed by reverse osmosis or deionizing filtration”, and points planted tanks to Equilibrium because Replenish “contains sodium and chloride, which can be harmful to plants”. One r/axolotls owner doses both in RO water and notes they raise GH “but not KH”.
Specs (linked: 500 mL)
- Dose: 5 mL per 10 US gal for +2.8 dGH (Seachem)
Pros
- A capful dose by volume, with no weighing
Cons
- Contains sodium chloride, so Seachem advises it for tanks without live plants
Brightwell Remineraliz-P, Powder for RO, DI or distilled
250 g · 2 g per 5 gal for about 2.7 dGH from 0 GH
Planted or community tanks on distilled or RO/DI water.
$15.90 from AmazonAs of Nov 2, 17:35 UTCVerdict
A powder labeled for distilled, RO and DI water.
Evidence: No independent test; owner reports. r/discus owner: Remineraliz-P, size not stated.
Brightwell says Remineraliz-P “reconstitutes reverse osmosis, deionized or distilled water” for “all freshwater planted and community aquaria”. Dissolved first, 2 g per 5 gallons adds about 2.7 dGH to water starting at 0 GH. One r/discus owner with a 114-gallon discus tank says Brightwell told them a teaspoon holds 2.18 g.
Specs (linked: 250 g)
- Dose: 2 g per 5 US gal for about +2.7 dGH, from 0 GH (Brightwell)
Pros
- Labeled for distilled water as well as RO and DI, per Brightwell
Cons
- Dosed by weight in grams, not by capful
Continuum Reconstitute RO, Dose set by fish type
500 mL · 1 capful to 4 tsp per 5 gal by fish
Discus, betta or livebearer tanks on RO, DI or distilled water.
$14.37 from AmazonAs of Nov 2, 17:35 UTCVerdict
GH and KH liquid dosed by the fish you keep.
Evidence: No independent test; maker specs. Source: Continuum Aquatics.
Continuum says Reconstitute RO adds GH, KH and trace minerals to RO, DI or distilled water. Per 5 gallons: 1 capful for discus and soft-water fish, 2 capfuls for “angelfish, bettas, barbs and general freshwater fish”, 4 teaspoons for goldfish, Central American cichlids and livebearers. It “will raise TDS more than it will raise GH”, so for harder-water fish Continuum says to measure both GH and TDS.
Specs (linked: 500 mL, liquid)
- Dose: 1 capful (about 1 tsp) to 4 tsp per 5 US gal, by fish type (Continuum)
Pros
- A dose chart by fish type, bettas and livebearers included, per Continuum
Cons
- Neither Continuum’s page nor the listing gives a GH or KH rise per capful
Brightwell NeoTiger KH+/GH+, Neocaridina shrimp minerals
250 mL · 2 mL per 5 gal for 1 dGH
Neocaridina or Tiger shrimp keepers on RO/DI water.
$11.32 from AmazonAs of Nov 2, 17:35 UTCVerdict
Made “for Neo Caridina and Tiger Shrimp, primarily”, per Brightwell; one owner reports KH stayed low.
Evidence: No independent test; owner reports. r/shrimptank owners: NeoTiger KH+/GH+, size not stated.
Per Brightwell, 2 mL of NeoTiger KH+/GH+ per 5 gallons of RO or DI water adds 1 dGH and 0.57 dKH. In an r/shrimptank thread, an owner who mixed to 7 dGH expected about 4 dKH but measured “less than 1”; another had “this exact same problem”. Test KH after mixing.
Specs (linked: 250 mL)
- Dose: 2 mL per 5 US gal for +1 dGH and +0.57 dKH (Brightwell)
Pros
- Made for Neocaridina and Tiger shrimp, with GH and KH figures per mL, per Brightwell
Cons
- One owner thread reports KH well below Brightwell’s figure
Aquatic Life RO Buddie 4-Stage, Compact entry RO/DI unit
50 GPD · Up to 50 gal a day at 65 PSI
Small freshwater tanks that need RO/DI water.
$69.99 from AmazonAs of Nov 2, 17:35 UTCVerdict
Four stages, up to 50 gallons a day, per Aquatic Life.
Evidence: No independent test; owner reports. r/Aquariums owner: RO Buddie, model not stated.
Aquatic Life says the RO Buddie +DI has sediment, carbon, membrane and DI resin stages, makes “up to 50 gallons in a 24-hour period” at 65 PSI and 77°F, and lists “smaller aquariums” among its uses. The Amazon listing says its carbon block “won’t remove chloramines”. One r/Aquariums owner, model not stated, reports “zero issues with my RO Buddie”.
Specs (linked: 4-stage RO/DI, 50 GPD)
- Output: up to 50 gal a day at 65 PSI and 77°F (Aquatic Life)
- Warranty: 1-year limited (listing)
Pros
- Color-changing DI resin shows when it needs replacing, per the listing
Cons
- The carbon stage won’t remove chloramines, per the listing
LiquaGen 5-Stage RO/DI, Portable reef-style RO/DI
75 GPD · Made for city water up to 300 TDS
Reef and freshwater keepers on city water.
$159.99 from AmazonAs of Nov 2, 17:35 UTCVerdict
Five stages and 75 GPD, per LiquaGen.
Evidence: No independent test; maker specs. Source: LiquaGen.
LiquaGen says its 5-stage unit is “designed primarily for reefers but can be used for fresh water or salt water”, needs no drilling, and is made “for city water use” with incoming TDS no higher than 300.
Specs (linked: 5-stage RO/DI, 75 GPD)
- Output: 75 GPD (LiquaGen)
- Warranty: 2 years (LiquaGen)
Pros
- Two carbon stages ahead of the membrane, per the listing
Cons
- Made for city water up to 300 TDS, per LiquaGen
iSpring RCC1D, High-output tankless RO/DI
150 GPD · DI stage for 0-1 TDS water
Large or several tanks, and reefs, that need RO/DI water in volume.
$190.31 from AmazonAs of Nov 2, 17:35 UTCVerdict
A 150 GPD membrane, the highest rating of the three units here, per their makers.
Evidence: No independent test; maker specs. Source: iSpring.
iSpring says the RCC1D has no tank or faucet, three pre-filters that “protect the RO membrane from chemicals like chlorine and chloramines”, and a DI stage for “0-1 TDS water”. A pump version, the RCC1DP, is sold for low water pressure. Unlike Aquatic Life, LiquaGen and iSpring give no test pressure or temperature for their ratings on the pages we read.
Specs (linked: RCC1D, 150 GPD tankless)
- Output: 150 GPD membrane (iSpring)
- Warranty: 1-year limited (iSpring)
Pros
- A 150 GPD rating, against 75 and 50 GPD for the other two units, per their makers
Cons
- The top price tier of the eight picks, with no storage tank included
Who should buy it
Large or several tanks, and reefs, that need RO/DI water in volume.
Which Water Should You Use?
Each water source type needs its own preparation; for RO, DI and distilled water that means remineralization.
| Water | What the sources say | What it needs |
|---|---|---|
| Tap | Suits most freshwater tanks (Culligan) | A dechlorinator (EPA) |
| RO or RO/DI | Useful for sensitive and saltwater fish (Culligan) | Usually minerals added back |
| Distilled | “should not usually be used by itself” (Culligan) | Remineralizing or blending |
| Bottled or spring | Mineral content “varies widely by brand” (Culligan) | Testing before use |
| Well | May carry hardness, iron or nitrates (Culligan) | Testing; aeration (Long’s EcoWater) |
Boiling “does not remove monochloramine”, per the EPA. Test GH, KH, pH and ammonia with a freshwater test kit; see also high pH and high nitrate. If fish look unwell, test the water and contact an aquatic veterinarian.
Frequently Asked Questions
Q. What is the best water to put in a fish tank?
For most freshwater fish, dechlorinated tap water, per Culligan and the top Reddit reply.
Q. Should I use tap or filtered water for a fish tank?
Culligan says to treat “tap water and filtered tap water” for chlorine and chloramine.
Q. What is the best bottled water for a fish tank?
Culligan and Long’s EcoWater say bottled and spring water vary in minerals; test it first.
Q. Is distilled or purified water better for fish?
Culligan says distilled water lacks “essential minerals and buffering capacity”. On Reddit, one reply prefers purified water for keeping its minerals; another notes “purified” water “can mean anything”.
Q. What is the best water for a betta fish tank?
Conditioned tap water, or RO or distilled water with minerals added back; Continuum doses 2 capfuls per 5 gallons for bettas.
Q. Why is my new aquarium water cloudy or milky?
Apart from Equilibrium’s brief haze, see why aquarium water turns cloudy. Also see our beneficial bacteria, bottled bacteria and cycling bacteria guides.
The bottom line
Final Verdict
Tap water needs a dechlorinator (conditioner guide). RO, DI or distilled water needs minerals back: Seachem Equilibrium (check price) for planted tanks, Seachem Replenish (check price) without plants, Continuum Reconstitute RO (check price) by fish type, Brightwell NeoTiger KH+/GH+ (check price) for shrimp. To make it: Aquatic Life RO Buddie 4-Stage (check price) for smaller aquariums, iSpring RCC1D (check price) for volume.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
