TDS for shrimp, explained
TDS is the number shrimp keepers check most often, because a TDS pen gives an answer in seconds. It is also the number most often misread. A TDS reading tells you how much is dissolved in your water, but not what it is. Used the right way, it is the quickest tool you have for keeping water changes consistent. Used on its own, it can hide a GH or KH problem. This guide explains what TDS means, the ranges commonly cited for shrimp, why it drifts, and how to put a TDS meter to work alongside your GH and KH tests.
What TDS actually measures
TDS stands for total dissolved solids: minerals, salts and other substances dissolved in the water, reported in parts per million (ppm), which is the same as mg/L. Hobby TDS pens do not weigh anything. They measure how well the water conducts electricity and convert that into an estimated ppm using a built-in factor. That has three consequences:
- It is one number for everything. Calcium and magnesium (GH), carbonate (KH), sodium, nitrate, fertilizer and remineralizer all add to it, and the meter cannot tell them apart.
- It mostly sees things that carry a charge. Dissolved salts and minerals register; many organic substances barely do. A low reading does not prove water is clean or safe, and it says nothing about ammonia or nitrite levels on its own.
- Meters differ. Different conversion factors and calibration mean two pens can read the same water differently. Compare your own readings over time rather than matching someone else's number exactly.
Why a TDS meter cannot replace GH and KH tests
Two tanks can read the same TDS and be very different for shrimp. One might be mostly calcium and magnesium, which shrimp need to molt; another might be mostly carbonate or sodium with very little GH, which is commonly linked to failed molts. That is why the usual advice is to confirm GH and KH with a drop test first. Once you know they are right, TDS becomes a fast way to see whether anything has changed. The test kit guide compares drop kits, strips and TDS pens.
| TDS | GH | KH | |
|---|---|---|---|
| Measures | Everything dissolved (estimated) | Calcium and magnesium | Carbonate and bicarbonate |
| Usual tool | Digital TDS pen | Liquid drop test | Liquid drop test |
| Best used for | Quick consistency checks, mixing water, acclimation | Molting minerals | pH stability |
| Cannot tell you | What is dissolved | KH or other salts | GH or other salts |
Commonly cited TDS ranges
| Shrimp | TDS (rough) | Notes |
|---|---|---|
| Cherry and other Neocaridina | About 150–250 ppm | Some sources go up to about 300 ppm. Often kept in suitable tap water. |
| Crystal, bee and other Caridina | About 100–160 ppm | Usually remineralized RO water on active soil, with GH about 4–6 and KH about 0–1. |
| Amano and ghost shrimp | Tolerant of a fairly wide range; stability matters most (see Amano and ghost shrimp care) | |
These are hobby guidelines, not hard limits, and sources differ. Many colonies do well in steady water slightly outside them. Owner reports link losses far more often to sudden swings than to a reading that is a little off. For a full setup, see the cherry shrimp care guide.
Why TDS rises between water changes
- Evaporation. Water evaporates, but minerals stay behind, so the tank slowly concentrates. Topping off with tap water adds more minerals on top. Top off with RO or distilled water instead.
- Food and waste. Breakdown products such as nitrate add to TDS over time, which is one reason regular partial water changes matter.
- Fertilizers, remineralizers and additives. Every dose adds dissolved solids. A jump right after dosing is expected; a steady climb means you are adding more than water changes remove.
- Rocks, substrate and decor. Calcium-rich rock, crushed coral or some substrates dissolve slowly and push TDS (and GH and KH) up.
A slow rise is normal. A sudden jump that you cannot explain, especially with shrimp acting oddly, is worth a closer look: test ammonia, nitrite, GH and KH, look for uneaten food or a dead animal, and check what was added recently. If shrimp are already dying, start with why are my shrimp dying.
How to use a TDS meter
- Rinse the probe in the water you are testing.
- Dip it to the marked depth and wait for the reading to settle.
- Test at a consistent time, for example just before a water change, so readings are comparable.
- Check calibration now and then with a calibration solution if your meter supports it, and replace the battery when readings wander.
- Write it down. The trend matters more than any single number.
Most pens compensate for temperature automatically, but very cold or warm samples can still read slightly differently, so test new water and tank water at similar temperatures.
Using TDS to mix RO and tap water
When you dilute tap water with RO or distilled water, TDS falls roughly in proportion to the mix. That makes TDS a handy guide for finding a recipe:
- Equal parts of tap water and RO roughly halves TDS, GH and KH.
- To hit a target, the fraction of tap water is about (target − RO reading) ÷ (tap reading − RO reading). For example, tap at 300 ppm, RO at 10 ppm and a target of 180 ppm works out to about 0.59, or roughly 6 parts tap to 4 parts RO.
Then confirm GH and KH with a drop test, because TDS only tells you the total. Once you have a recipe, the TDS pen is a quick check on each new batch. If you remineralize pure RO water instead, mix the remineralizer into a bucket, check TDS and GH, and follow the product's own dosing directions.
Keep water changes matched
The most useful habit is simple: before a water change, test the tank and the new water. Aim for new water within a small margin of the tank, then make a modest, temperature-matched change. If the tank has drifted far from your target, close the gap gradually over several changes rather than in one go. See shrimp tank water changes for a routine.
TDS is also the easiest way to judge acclimation. When new shrimp arrive, compare the bag water with your tank; the bigger the gap, the slower you should go. Drip acclimation explains how to use those readings.
Track it
Record TDS at every water change, with GH and KH monthly once things are steady. The Water Parameter Log printable keeps TDS, GH, KH, pH and temperature on one page, so slow drift is easy to spot.
Frequently asked questions
What does TDS mean in a shrimp tank?
TDS stands for total dissolved solids: an estimate, in ppm, of everything dissolved in the water, including minerals, salts, fertilizer and waste products. A TDS pen estimates it from electrical conductivity.
What TDS do cherry shrimp need?
Cherry shrimp and other Neocaridina are commonly kept at roughly 150–250 ppm, with some sources going up to about 300 ppm. Steady water matters more than an exact number.
What TDS is good for crystal red shrimp?
Crystal, bee and other Caridina are commonly kept at roughly 100–160 ppm, usually on remineralized RO water and active soil. Check GH and KH as well.
Can a TDS meter measure GH or KH?
No. It reports one number for everything dissolved and cannot tell calcium from carbonate or sodium. Confirm GH and KH with drop tests, then use TDS for quick consistency checks.
Why does my shrimp tank TDS keep going up?
Evaporation concentrates minerals, and food, waste, fertilizers and remineralizers all add dissolved solids. Top off with RO or distilled water and keep up regular partial water changes.
How do I lower TDS in a shrimp tank?
Do gradual water changes with water that has a lower TDS, such as tap water mixed with RO or distilled water, and top off evaporation with RO or distilled water. Lower it over several changes rather than all at once.