TDS is the first number we check on any tank that's behaving oddly, and one of the first we'd hand a beginner. Understanding TDS for shrimp comes down to a single shift: read it as a trend, not a target. On its own a total dissolved solids reading won't diagnose anything, but it tells you something has changed — usually before your shrimp show it. That makes it the closest thing shrimp keeping has to an early-warning light.
What TDS actually measures
TDS stands for total dissolved solids: everything dissolved in your water, added up into one number in parts per million (ppm). Calcium and magnesium, carbonates, sodium, nitrate, trace salts — a TDS pen lumps them all together and hands you a single figure.
That's both its strength and its limit. One number is quick to read and easy to track, but it won't tell you what is dissolved in there. Two tanks can each read 220 ppm with completely different chemistry — one rich in the calcium and magnesium shrimp need for their shells, the other carrying the same total as sodium and nitrate that do them no good at all. So TDS never replaces your GH and KH tests; it sits alongside them, and its real job is spotting change.
Think of it as the water's overall mineral load. In a stable tank that load barely shifts from one week to the next. When it starts to move, that movement is your signal. How TDS fits together with pH, GH, KH and temperature is laid out in full in our Neocaridina water parameters guide.
What TDS should cherry shrimp have
For a cherry shrimp colony, aim for TDS 150–250 ppm. If you're breeding and want the fastest, healthiest broods, the sweet spot narrows to roughly 180–250. Below about 150 there often isn't enough dissolved mineral for shrimp to build shells reliably, which surfaces as moulting trouble; well above 250 and you're usually looking at mineral build-up that has crept in over time.
The band is deliberately wide because, as with every shrimp parameter, stability beats hitting a magic figure. A colony sitting steady at 240 will do better than one bounced between 160 and 260 by heavy-handed dosing. Pick a sensible number inside the range, then defend it.
Where you naturally land depends on your tap water. Hard-water regions — London and much of the South East — often come out of the tap already up around 250–300 ppm, comfortably minerally. Soft-water regions read far lower and need remineralising to reach range. Our UK tap water guide has the regional detail; the point here is that your starting TDS is a fact about your postcode before it's ever a choice.
Read TDS as a trend-line, not a snapshot
This is the part that turns a TDS pen from a gadget into a genuinely useful tool. A single reading, taken cold, barely means anything. The same reading logged every week means almost everything.
Get into the habit of testing at the same point in your routine — we check just before the weekly water change — and jotting the number down. A phone note or a scrap of paper taped by the tank is plenty. After a month you'll have a baseline: this tank runs at, say, 220, give or take a little. From then on you're no longer asking "is 220 good?" — you're asking "is this tank still doing what it always does?"
Two kinds of movement matter, and they mean very different things. A slow creep upward over several weeks is one story. A sudden jump or drop between two readings is another entirely. Learning to tell those two apart is most of the value a meter gives you.
When TDS creeps up slowly
A gradual climb — a few ppm a week, quietly adding up over a month or two — almost always comes down to concentration. Water leaves; minerals stay.
Evaporation is the usual culprit. When tank water evaporates it leaves its dissolved minerals behind, so the TDS of what remains rises. Topping up with more tap water, which carries its own minerals, only compounds it. The fix is to top up evaporation with dechlorinated RO or rainwater — adding volume without adding solids — and to keep a lid on to slow the evaporation in the first place.
Overfeeding is the other big driver. Uneaten food and the waste it generates dissolve into the water as extra load, nudging TDS up while also feeding the other problems of overfeeding: planaria, snail booms, fouled water. A creeping TDS in a well-topped-up tank is often the very first sign you're putting in too much food.
Slow mineral build-up rounds it out: infrequent or too-small water changes let dissolved solids accumulate faster than they're exported. The cure for a slow creep is rarely dramatic — a run of modest, regular water changes with correctly remineralised water walks the number back down gently. What you must not do is panic and slash it in one hit, because the swing is far worse than the drift.
When TDS jumps suddenly
A sharp move between readings means something happened, and it's worth working out what before you touch anything.
Common causes of a sudden rise: a heavy remineraliser dose (easy to overshoot if you tip it straight into the tank rather than into premixed change water), a new rock or piece of hardscape leaching minerals — limestone and some seiryu-type stones raise hardness and TDS steadily — or an animal that has died and started to decay unnoticed. A sudden drop, meanwhile, usually means a large water change with under-mineralised water, or a heavy top-up that simply diluted things.
Whatever the cause, the danger with a sudden change often isn't the new number itself — it's the speed of getting there. A fast TDS swing is exactly the kind of shock that triggers a bad moult and the white ring of death. So when you spot a jump, resist the urge to haul it straight back. Correct it the way you'd correct any parameter: gradually, with small measured water changes, letting the colony catch up. Then deal with the cause — reseat or remove the leaching rock, get your dosing right, find the body.
The TDS pen: the cheapest useful test you'll buy
You don't need a laboratory for any of this. A basic digital TDS pen — the pocket kind you dip in for a second — is the least expensive meaningful test tool in the hobby, and the one we'd tell a new keeper to buy first after a dechlorinator.
A few practical notes. Give it a moment to settle on a stable reading before you trust it. TDS shifts a little with temperature, so compare like with like — testing tank water and top-up water at roughly the same temperature. And every pen drifts eventually; the better ones can be recalibrated against a known solution, which is worth doing now and then if your numbers start looking strange. If you keep shrimp in a soft-water area and mix your own water, a TDS pen stops being optional altogether — it's how you dose to a target instead of guessing, as covered in our remineralising guide.
None of this is much work. Dip, read, write it down, once a week. That thirty-second habit is what turns TDS from a number you vaguely know into the early-warning system it's meant to be. Fold it into the rest of the routine in our cherry shrimp care guide and you'll catch most trouble long before it ever costs you shrimp.
FAQ
What TDS is best for cherry shrimp?
Aim for TDS 150–250 ppm for a general cherry shrimp colony, and 180–250 if you're breeding and want the strongest broods. The exact figure inside that band matters less than holding it steady — a stable 240 beats a number that swings around. Below roughly 150 there's often too little mineral for reliable moulting; much above 250 usually signals mineral build-up worth addressing.
Can TDS be too high for shrimp?
Yes. Once you're pushing well past 250 ppm, especially if it has crept there over time, shrimp can struggle to moult cleanly and breeding slows. The bigger risk, though, is often how you fix it: dropping TDS fast with a big water change causes a swing that's more dangerous than the high reading itself. Bring it down gradually with small, regular changes instead.
Why does my shrimp tank TDS keep rising?
A slow, steady rise is nearly always concentration. Evaporation leaves minerals behind as the water level drops, so top up with dechlorinated RO or rainwater rather than more tap water. Overfeeding and infrequent water changes add to it. If the climb is gradual, address the cause and walk it back with modest weekly changes — don't crash it down in one go.
Do I really need a TDS meter for shrimp?
It's the single most useful cheap test you can own, so we'd say yes — especially in soft-water areas where you remineralise your own water and need to dose to a target. A pocket TDS pen costs little, reads in seconds, and its real power is tracking the trend week to week. It won't replace your GH and KH tests, but it will flag trouble first.