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Two questions come up constantly in shrimp keeping: “how much RO do I mix with my tap water?” and “will this water change shock my shrimp?”. This calculator answers both with simple mixing math, so you can plan a batch or a change before you pour anything.
The math behind it
- Mixing: the fraction of tap water = (target TDS − RO TDS) ÷ (tap TDS − RO TDS). Everything dissolved in tap water, including GH and KH, is diluted by the same fraction.
- After a change of p%: new TDS = tank TDS × (1 − p) + new water TDS × p.
- Repeated changes close the gap by the same fraction each time, which is why several small changes are gentler than one big one.
Typical targets
| Shrimp | Target TDS | Usual water source |
|---|---|---|
| Neocaridina | 150–250 ppm | Dechlorinated tap, or RO + GH/KH remineralizer |
| Crystal / Taiwan bee | 100–160 ppm | RO + GH-only remineralizer (KH 0) |
| Tiger | 130–250 ppm | RO + remineralizer, sometimes blended |
FAQ
Why not just use diluted tap water for Caridina?
Diluting tap water lowers TDS but keeps its KH ratio, and most tap water carries enough KH to push pH above what Caridina want. That’s why bee shrimp keepers start from pure RO.
How big a TDS swing is safe?
Many breeders keep each change’s swing under about 10%. Match temperature too — a big temperature drop plus a TDS drop is a classic molt trigger.
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