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Total dissolved solids (TDS) is a very interesting and misunderstood water parameter in shrimp keeping. For example, you test your shrimp tank and get a TDS reading of 350 ppm. Is this good or bad? The answer depends on information most guides never explain.
TDS can be a very useful measurement in many shrimp keeping situations – it can also be entirely misleading and cause chaos for shrimp keepers. Let’s dive into the science behind TDS – what it’s measuring, why certain ranges are recommended for a shrimp species, and when TDS measurements are useful. We’ll also learn about the relationship between TDS and conductivity - a more common measurement type for European shrimp keepers.
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The following increases TDS:
The following decreases TDS:
The most controlled setting possible for shrimp keepers is to use purified water with a remineralizer (a product that increases GH and sometimes KH). RO/DI water may start with 5 ppm of TDS – a very small amount of unknown substance that is typically harmless -which we then increase by adding enough remineralizer to get the desired GH/KH range. In this example, let’s say we remineralize to 71 ppm of GH (4 dGH) and 0 KH for a Blue bolt Caridina shrimp tank. This means we would expect a TDS of around 76 ppm after remineralization, including the initial TDS of the RO/DI water. We will never quite see the TDS calculated from adding together GH/KH because remineralizers always have additional salts to balance them out, which increases the TDS.
Image Description - A comparison of the TDS ranges of different types of water. RO stands for Reverse Osmosis. RO/DI water stands for Reverse Osmosis + Deionization for additional purification.
Each remineralizer has a slightly different blend of salts so what’s important is knowing what TDS our particular remineralizer reaches. In this case, our remineralizer raises the TDS to 90 ppm at 4 dGH. Since we know that, we can now use a TDS meter during water changes to quickly and easily measure whether we’ve remineralized new water to the right GH, rather than using the slightly less convenient liquid test kits. The first time using a new remineralizer does require testing GH/KH, but a TDS meter may be used every time after that. The benefit of TDS is the speed and ease with which we can get information.
Now, let’s compare that experience to measuring TDS in a shrimp tank with tap water. Out of this hypothetical tap, the water has 71 ppm of GH and 0 ppm KH - just like the remineralized water from the previous example. The difference is that the total TDS is 450 ppm, meaning there’s around 375 ppm of TDS that’s unaccounted for. That could consist entirely of toxins like copper or nitrates, or it could be all sodium and relatively harmless. That’s why a single TDS measurement does not tell us any useful information about how healthy tap water is but the more we know about our water, the better we can analyze its quality.
We can also understand how the recommended TDS ranges for different shrimp species are calculated. Let’s take the recommended parameters for Neocaridina as an example:
| Neocaridina | ppm | dH |
|---|---|---|
| Recommended GH | 107-179 | 6-10 |
| Recommended KH | 36-143 | 2-8 |
Commonly, the recommended TDS range for Neocaridina is 200-300 ppm. The combined minimum values of GH and KH give us 143 ppm, while the combined maximum values give us 322 ppm. As we mentioned before, the salts that increase GH and KH always involve other solids that increase TDS, so even the lowest levels of the recommended GH/KH ranges will be higher than 143 ppm and typically close to the 200 ppm of TDS, which explains the low end of the recommended range.
As for the high end, 10 dGH and 8 dKH (322 ppm total) are relatively rare because most natural mineral sources for tap water and most commercial products increase GH/KH by a ratio of 2:1. This means that the 10 dGH upper limit tends to limit KH to around 5 dKH, giving us a combined 269 ppm. When accounting for the additional TDS of the salts required to achieve these GH/KH values, we arrive close to 300 ppm, which explains the upper limit of the recommended range.
These same calculations can be done with other shrimp species to understand their recommended TDS ranges.
Again, surpassing this upper TDS limit is not necessarily a bad thing but the risk depends on the shrimp species. Hardier species like Neocaridina are not very sensitive to TDS, so they are often kept at 400-500 ppm without issue – assuming there are no dangerous levels of pollutants in the water, which is difficult to determine with tap water. With remineralized RO/DI water guaranteed to have no pollutants, we’ve kept Neocaridina at 600+ ppm (30+ dGH) without issue because the water is healthy and the mineral ratios are balanced.
On the other hand, more sensitive species and breeds of Caridina shrimp are affected by TDS outside of the range they are bred in. They can adapt to higher ranges assuming the water is healthy (right mineral ratios, low nitrates, etc.) but it does seem to be less likely. Newer breeds of Caridina like Blue BOAs are especially sensitive to TDS. Our hypothesis is that this sensitivity is a result of inbreeding depression, which should improve over time as breeders work to reduce inbreeding.
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From monitoring changes in water quality to quickly checking if we've added enough remineralizer, TDS can be a very useful tool to ensure the health of our shrimp tanks. The key is understanding that TDS is only as meaningful as the context we provide it. A reading of 350 ppm could indicate perfectly healthy water in a remineralized RO/DI setup, or it could be a warning sign in tap water with unknown dissolved substances.
Remember the two golden rules: TDS is most valuable when tracked over time, and it becomes exponentially more useful the more we know about our water's composition. Whether you're troubleshooting sudden changes, streamlining your remineralization process, or simply wanting to better understand your shrimp's environment, a $15 TDS meter paired with knowledge of your GH and KH values puts you ahead of most shrimp keepers.
The biggest mistake we see is shrimp keepers panicking over TDS readings without considering what's actually dissolved in their water. Don't let a number dictate your actions – let your understanding of that number guide your decisions. Your shrimp will thank you for it.
Pssst... Want to learn everything you need to know to have happy and healthy freshwater shrimp? We've got you covered with clear, concise, and fun information in every lesson of The Shrimp School!
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