Shrimp keepers building water from RO or distilled water need to add minerals back precisely, because both too little and too much TDS stress sensitive caridina and neocaridina. This calculator turns your starting TDS, target, and volume into an exact remineralizer dose in grams, so each water change lands on the same parameters.
How it works
The dose follows directly from how much you need to raise TDS and how strong the product is:
rise needed = target TDS − starting TDS
grams = rise needed × volume(L) / dose strength
dose/L = grams / volume(L)Dose strength is the ppm of TDS each gram raises in one litre, taken from the product spec. Because remineralizer only adds dissolved solids, the rise must be positive — if your target is lower than the current TDS, the only way down is to dilute with more pure water.
Caridina vs. neocaridina: why target TDS matters
The two main shrimp groups have very different water chemistry needs, and TDS is the easiest daily measurement to track:
| Shrimp type | Typical TDS target | KH preference |
|---|---|---|
| Caridina (Crystal Red, Taiwan Bee) | ~100–130 ppm | Very low, often near 0 |
| Neocaridina (Cherry, Blue Velvet) | ~150–250 ppm | Moderate |
Caridina species evolved in Sulawesi crater lakes and southern China mountain streams — soft, mineral-poor water. They tolerate very little carbonate hardness. Most keepers use a GH+ product (no KH) for caridina so the TDS is built purely from magnesium and calcium without driving up KH and pH. Neocaridina are hardier and do well with a combined GH/KH+ product.
Worked example
You are mixing 20 litres of RO water (starting TDS 3 ppm) to a caridina target of 130 ppm, using a GH+ salt with a dose strength of approximately 100 ppm per gram per litre:
- Rise needed: 130 − 3 = 127 ppm
- Total grams: 127 × 20 ÷ 100 = 25.4 grams
- Per litre: 25.4 ÷ 20 = 1.27 grams/litre
Always add the remineralizer to the mixing bucket first, dissolve thoroughly with agitation, allow a few minutes to stabilise, and then confirm with your TDS pen. Batches vary slightly, and the meter has the final word.
Why tap water does not work for this calculation
Tap water has variable mineral content — often 100–400 ppm depending on your region — and that baseline shifts with the seasons and the local treatment plant. Remineralizing tap water means trying to raise an uncertain starting point to a target, which produces inconsistent results and can cause TDS swings between water changes. Starting from RO or high-quality distilled water at near-zero TDS is the only way to make this calculation reliable.
After mixing: how to do water changes precisely
For a consistent shrimp tank, batch-mix your change water in a dedicated bucket before every water change rather than calculating the dose on the fly. Keep the same remineralizer product, the same bucket size, and the same target TDS so every change is identical. If your RO membrane starts degrading, the starting TDS will creep up — remeasure regularly and adjust the dose. Even a ten-point TDS swing between water changes can trigger moulting stress in caridina.