Remineralizing RO water for shrimp

By the Shrimp Tank Hub editorsUpdated Oct 23, 2026Research-based

Reverse osmosis (RO) water is the blank canvas of the shrimp hobby. An RO unit strips out almost everything, including the calcium and magnesium shrimp need to molt, so on its own it is not suitable for a shrimp tank. Add the right minerals back and you get water that is exactly the same every time, whatever your tap water is doing. This guide explains the targets for the two main groups of dwarf shrimp, the two kinds of remineralizer, and a simple bucket method for mixing water you can repeat at every water change.

Why RO water needs remineralizing

RO units push water through a very fine membrane, and RO/DI units add a deionizing resin stage that removes even more. Distilled water is similarly bare. That is useful, because it removes the hardness, nitrate, metals and other variables that come with tap water. But it leaves water with almost no GH and no KH:

• No GH means no dissolved calcium or magnesium. Shrimp use these minerals to harden each new shell, and hobby references commonly link very soft water to failed molts. See shrimp dying after molting.
• No KH means no buffer, so pH can swing with very small changes. That suits Caridina on an active soil, which sets the pH itself, but not Neocaridina on gravel or sand.

Remineralizing puts back a controlled amount of exactly what shrimp need. The full background on what each number means is in GH and KH explained and TDS explained.

Targets for Neocaridina and Caridina

These are commonly cited hobby ranges, and sources differ by a degree or two. Many colonies do well in steady water just outside them. Shrimp losses are linked far more often to sudden changes than to a reading that is slightly off, so pick a target inside the range and keep every batch the same. Caridina need RO-based water far more often than Neocaridina, which do well in many treated tap waters; see can shrimp live in tap water.

GH-only vs GH/KH remineralizers

Shrimp remineralizers come as powders or liquids, and most fall into one of two types. Brand names vary, but the label usually says which kind it is (often "GH+" for GH-only and "GH/KH+" for the combined type).

A few points matter more than the brand:

• Match the type to your shrimp and substrate. A GH/KH product in a Caridina tank on active soil fights the soil. A GH-only product in a Neocaridina tank on plain gravel leaves almost no buffer, so pH can drift low and swing. Some Neocaridina keepers do use GH-only water on active soil, but it is not the simple, stable default.
• Products are not interchangeable gram for gram. Each has its own dose and its own ratio of TDS to GH, so a recipe for one brand does not carry over to another. Always start from the label.
• Look for a shrimp-specific product. General aquarium buffers and "pH up" products often add mostly KH and sodium, not the calcium and magnesium shrimp need.

If you are shopping, browse shrimp GH-only remineralizers or GH/KH remineralizers, and choose by type first.

How to remineralize RO water, step by step

1. Check the source water. Test your RO, RO/DI or distilled water with a TDS pen. It should read very low, typically single digits. A reading that keeps creeping up usually means the RO membrane or DI resin needs replacing.
2. Use a clean, food-safe container kept only for aquarium water, and measure the volume. Marking the bucket at 1 or 2 gallons saves guessing later.
3. Dose by the label. Add the remineralizer at the product's directed rate for your target. If you are new to the product, start at the low end; it is easier to add a little more than to take it out.
4. Dissolve it fully. Stir well, or run an air stone or small powerhead for a while. Powders can cloud the water briefly; let it clear before testing.
5. Test GH (and KH). Use a liquid drop test for GH, plus KH if you used a GH/KH product. Adjust with a little more mineral or a little more RO until you hit your target.
6. Read the TDS and write it down. Note the product, amount, volume, GH, KH and TDS. That is your recipe.
7. Match the tank before it goes in. Bring the new water to tank temperature and check that its TDS is close to the tank's. If the tank has drifted, close the gap gradually over several changes rather than all at once.

Using TDS to repeat your recipe

Once you have confirmed GH and KH with drop tests, the TDS pen becomes your fast check. Because you start from near-zero water and add only one product, the TDS of each batch tracks how much product you added. If your recipe gave, say, 6 dGH at a certain TDS reading, the next batch that reads the same TDS on the same product almost certainly has the same GH. That is why many Caridina keepers simply remineralize to a TDS number and confirm GH with a drop test now and then.

This only works with a known recipe. TDS cannot tell calcium from carbonate or sodium, so if you change products, add fertilizer to the bucket or mix in tap water, go back to drop tests. The test kit guide covers drop kits and TDS pens.

Mixing RO with tap water instead

For Neocaridina, you do not always need to remineralize pure RO. If your tap water is safe once dechlorinated but too hard, mixing it with RO dilutes everything in roughly the same proportion: equal parts tap and RO roughly halves GH, KH and TDS. The TDS guide has a simple formula for hitting a target. Caridina usually need pure remineralized RO, because most tap water carries KH that works against active soil.

Top-offs, storage and water changes

• Top off evaporation with plain RO or distilled water, not remineralized water. Minerals stay behind when water evaporates, so topping off with mineralized water slowly pushes GH, KH and TDS up.
• Use remineralized water for water changes, matched to the tank's current TDS and temperature.
• Mix ahead. Mixing the day before, in a covered container with an air stone or heater if needed, gives minerals time to dissolve and the water time to reach tank temperature.
• Keep changes modest and regular. Steady small changes with identical water are what make RO setups so stable. See shrimp tank water changes for a routine.

Common mistakes

• Putting pure RO straight into the tank for water changes. It drops GH and TDS suddenly; always remineralize first (top-offs are the exception).
• Using baking soda to raise GH. Baking soda raises KH and pH, not GH, and adds sodium.
• Using household softened water. Softeners swap calcium and magnesium for sodium, which is the opposite of what shrimp need.
• Using the wrong type, such as a GH/KH product over active soil for Caridina.
• Chasing numbers. Changing the recipe every week causes more trouble than a target that is slightly off. Pick one recipe and keep it.
• Trusting TDS alone after changing something. A new product or additive means new drop tests.

If shrimp are already dying, start with why are my shrimp dying, and acclimate new shrimp slowly to remineralized water with drip acclimation.

Track it

Write your recipe and every reading down. The Water Parameter Log printable keeps GH, KH, TDS, pH and temperature on one page, so you can repeat a recipe exactly and spot slow drift early.

Frequently asked questions

Can shrimp live in pure RO water?

No. Pure RO or distilled water has almost no calcium, magnesium or carbonate, so shrimp cannot get the minerals they need to molt and pH is unstable. Remineralize it before using it for water changes; plain RO is fine for topping off evaporation.

What GH and KH should remineralized water have for cherry shrimp?

Cherry shrimp and other Neocaridina are commonly kept at about 6–8 dGH and 2–6 dKH, with TDS roughly 150–250 ppm. A GH/KH remineralizer reaches both from RO water.

What should I remineralize RO water to for crystal shrimp?

Crystal, bee and other Caridina are commonly kept at about 4–6 dGH and 0–1 dKH, with TDS roughly 100–160 ppm, on active soil. Use a GH-only remineralizer so you do not add KH.

What is the difference between GH+ and GH/KH+ remineralizers?

A GH-only (GH+) remineralizer adds calcium and magnesium without carbonate, so it raises GH and TDS but not KH. A GH/KH+ remineralizer also adds carbonate or bicarbonate, so it raises GH, KH and TDS.

Can I remineralize RO water to a TDS number?

Yes, once you know your recipe. With one product in near-zero water, TDS tracks the dose, so a batch at your usual TDS usually has your usual GH. Confirm with a GH drop test now and then, and always after changing products.

Should I top off with remineralized water?

No. Top off evaporation with plain RO or distilled water, because minerals stay in the tank when water evaporates. Use remineralized water only for water changes.