Planning a Shrimp Tank: What an Aquarium Simulator Can Predict

Before you buy a tank, it helps to see it first. You can check whether the wood fits, whether the plants crowd the glass, and whether the tank still looks open enough. Our free Aquarium Sim is a pixel-art planner built for that job. A simulator is a picture of a plan, though. It isn't a water test.

This post separates what a planning tool can tell you from what only your own water, room and patience can tell you. For the second group we use what the research on Neocaridina davidi (the species behind cherry, blue, and demon-type shrimp) actually says.

What a simulator is good at

Anything that is arithmetic or geometry is fair game. That includes tank volume, how much of the footprint is hardscape (rock and wood), where plants will shade each other, and whether a hiding spot is reachable. These are real planning questions, and it is far cheaper to find a problem on screen than after you've added water.

A simulator is also a good place to try the stocking math before you commit. The next sections show why that math is less simple than a "shrimp per gallon" rule.

Step by step: planning a tank in the Aquarium Sim

Here is one build from start to finish in the Sim's Beginner mode, which walks through six pages in order. Every picture below is a screenshot of the Sim, taken Nov 2, 2026.

1. Water, room and tank

Start with what you already have: your water source, how warm or cool the room runs, and the tank. The Sim also shows how much water is left once substrate and rock take their share. That is the arithmetic a planner does well. Your actual tap-water hardness is not something it can know, so test that separately.

2. Equipment

Gear comes before anything alive. When this same build was run without a filter, the Sim's results flagged "no filter and no aeration" as critical, which is the kind of mistake that is free to make on screen.

3. Scape it

Substrate, rock and wood decide where shrimp can graze and hide. Drag & drop lets you move each piece until the layout leaves open swimming room in front.

4. Plants

Plants add grazing surface as well as looks, and the research section below shows plant choice can change how shrimp grow and breed. Easy plants that need no CO2 are the safe start for a first tank.

5. Shrimp

As shrimp go in, the Sim shows a whole-tank waste load and a stocking range for the tank. Those meters are the Sim's planning estimates, not measured limits. The density section below explains why no study gives a safe shrimp-per-gallon number for a home tank.

6. Results

The results page scores the build and lays out a schedule: cycle first, add livestock only once ammonia and nitrite read zero, then regular partial water changes. The Sim labels its colony numbers as estimates, and your test kit, not the schedule, decides the day shrimp go in. The rest of this post is about those things a screen can't see.

What it can't see: your temperature

Neocaridina are eurythermal, meaning they tolerate a broad temperature range. A survey of feral populations in German waters found about a third of the shrimp collected were in water below 15°C (59°F). Ovigerous (egg-carrying) females turned up even below 10°C (50°F) [4].

That doesn't mean cold is ideal. In a lab study on juveniles, shrimp at 24°C grew more slowly than those at 28°C and 32°C at day 30 of a 90-day period. The researchers concluded the delay lasted only about 30 days after hatching [13]. Growth in crustaceans generally rises with temperature to a peak, then falls near the upper tolerance limit [13].

The warm end matters more than the cool end. In one study, ovarian maturation and spawning were seen at 28°C but not at 33°C [3]. Heat also lowers oxygen. Warm water holds less dissolved oxygen than cool water [6]. For reference, a UN Food and Agriculture Organization table lists fully saturated freshwater at 30°C (86°F) at 7.54 mg/L [7]. The same field survey found Neocaridina in water with as little as 3.1 mg/L, so they are not fragile about oxygen [4]. Heat still removes margin when something else goes wrong.

In a real tank: the number that matters is your room, not the setpoint on a screen. Many keepers find that a tank near a sunny window or in an unairconditioned summer room drifts far from its target. If you keep shrimp somewhere hot, plan for cooling and a thermometer you actually look at. A simulator doesn't know where you live.

Density: the 90-day study and its limits

The best-known stocking experiment is a 90-day lab study of cherry shrimp. Newly hatched juveniles were kept at 2.5, 5 and 10 shrimp per liter. At day 90, females at the lowest density weighed 45% more than females at the highest. Males at the lowest density weighed 29% more than males at either of the other two. Survival was high and unaffected by density [1]. The authors recommended 2.5 shrimp per liter to get larger females [2].

Three cautions apply when you turn that into a hobby rule:

• Units. 2.5 per liter is roughly 9.5 per gallon, and 10 per liter is roughly 38 per gallon. Those are dense lab-culture figures. No tested group was less crowded than that, so the study can't tell you what a lightly stocked planted tank looks like.
• Growth is not welfare. The study measured weight, survival, sex ratio and body composition. It found no survival penalty from crowding, but the abstract gives no details on filtration or water changes, so how much husbandry offset the load is unclear.
• It began with juveniles. A tank of mixed-age adults with a growing colony behaves differently from a single cohort.

So a simulator can multiply shrimp by gallons. The answer is not a safe limit. In a home tank the practical ceiling is how much waste your filtration, plants and feeding habits can handle, and that is the next section.

What it can't see: ammonia, pH and hardness

Ammonia is the waste product that most often decides whether a new tank works. It exists in water in two forms: un-ionized ammonia (NH3) and ammonium (NH4+). Together they make up "total ammonia nitrogen." The share in the un-ionized form rises with pH and temperature, and that form is about 100 times more toxic to fish than ammonium. Standard test kits measure only the total [5].

Note the limit of that evidence: the 100-times figure is for fish. None of the sources reviewed for this post gives a Neocaridina-specific lethal ammonia concentration. Hobby guides call for zero detectable ammonia and nitrite, and suggest stocking only after both hold at zero on consecutive tests [8]. That conservative target makes sense given how little is known. Our post on shrimp biofilm covers what a new tank is still missing in its first weeks.

Hardness is where hobby sources disagree most. GH (general hardness) measures dissolved calcium and magnesium. One guide gives GH 6–8 with a TDS (total dissolved solids) of 150–250 [8]. Another keeper's guide lists GH 4–10 dGH and says stability matters more than chasing an exact reading [9]. These are husbandry opinions rather than controlled studies. What a simulator can't do is read your tap water. You have to test that yourself, and your source water sets your starting point before you add anything.

What it can't see: volume and stability

Water volume buffers change. Say you add one gallon of water that differs from the tank's. In a 5-gallon tank, that gallon is about 17% of the total once mixed. In a 50-gallon tank it is about 2%. That is simple arithmetic, and it is why the same mistake does far less damage in a bigger tank.

Equipment failure has the same logic. One patent filing on small aquarium temperature control notes that a stuck thermostat or switch can rapidly push a small volume into lethal temperatures [12]. A patent is not research, but it matches the physics: less water means less thermal mass.

In a real tank: a small tank can work, but a larger one forgives more mistakes. If you're choosing between sizes, our aquarium collection is a good place to compare, and the extra gallons are cheap insurance.

Plants, moss and surfaces: more than decoration

Shrimp aren't passive occupants, and a layout decides what they have to graze. One lab study compared substrates and found that shrimp raised with Vesicularia (the genus of Christmas moss) reached their peak relative growth rate earlier and higher. Maximum size was similar across treatments. Shrimp raised with Ceratophyllum (hornwort) had only 10% ovigerous females, versus 30–48% in the other treatments [10]. It is one study in lab culture, so don't read it as a ban on hornwort. It does show that plant choice can change outcomes.

Shrimp also change the plants. A related species reduced the periphyton (the algae-and-microbe film) on Vallisneria leaves and the plants grew faster. The authors also flagged possible increases in nutrients and turbidity [11]. A static picture can't show that give-and-take.

A quick map: predictable vs. not

A practical sequence

1. Sketch the layout in the Aquarium Sim and check that the tank volume and stocking math work.
2. Test your tap water for GH, KH and pH before you pick anything else.
3. Set up the tank and let it cycle. Stock only when ammonia and nitrite read zero on consecutive tests [8].
4. Start with fewer shrimp than the arithmetic allows and let the colony grow into the space.
5. If a shrimp looks off after you've set up, our Para-Medic tool walks through the usual causes.

Most Neocaridina research is lab culture of cherry-type shrimp; results for other color lines in home tanks are assumed to be similar, not proven.