Amano Shrimp: The Algae Crew That Loves Hard Water

If I could only keep one invertebrate in a freshwater tank, it would be the Amano shrimp. They earn their place: a well-stocked group grazes hair algae and biofilm all day, they are tough enough to shrug off the sort of water that kills fussier shrimp, and my very hard tap water is closer to ideal for them than it is for most of the fish I keep. I have run Amanos in tanks reading about 22 dGH for years, alongside shell-dwellers and livebearers, and they have been some of the least demanding animals in the house.

The one thing nobody tells you clearly at the shop is that Amano shrimp are not the same proposition as cherry shrimp. You do not build a self-sustaining colony. You buy a working group, you keep it alive, and it slowly dwindles over years rather than replacing itself. Once you accept that, they are a joy.

What an Amano shrimp actually is

The Amano shrimp is Caridina multidentata, still sold under its old name Caridina japonica in plenty of shops. It comes from streams in Japan and Taiwan, and it reached the hobby largely through the aquascaper Takashi Amano, who used them by the hundred to keep planted tanks clean. That is where the common name comes from.

They are bigger than most dwarf shrimp, reaching about 4 to 5 cm as adults, which is part of why they are such good workers: they can tackle mats of algae that a cherry shrimp would take a week to nibble. The colour is a translucent grey-green with a broken line of dots and dashes down each side, and a pale stripe along the back. Females are larger and their dots tend to be longer dashes; males show rounder, more even spots. Kept well, they live around two to three years, sometimes longer.

Why hard water suits them

Here is where my tap water finally works in the livestock’s favour rather than against it. Most care sheets quote a general hardness of roughly 5 to 15 dGH for Amanos, but that figure is really a warning about the bottom end, not the top. Shrimp build their shells from minerals in the water, and a shrimp in soft water is a shrimp that struggles to moult. My tap runs about 22 dGH with plenty of calcium, and Amanos moult cleanly and often in it.

The parameters I actually keep them in:

• Temperature: 18 to 26°C. They are happiest cooler than most tropicals and genuinely dislike being cooked, so I keep their tanks at the lower end of the fish’s comfort range.
• pH: anywhere from about 6.5 to 8. Mine sits around 7.5 to 8 and they do not care.
• Hardness: hard is fine. If anything, hard water is an advantage for moulting.
• Ammonia and nitrite: zero, always. Like all shrimp, Amanos are far more sensitive to ammonia and to copper than fish are.
• Nitrate: I keep it under about 20 ppm with normal water changes.

If your water is soft, the honest fix is to remineralise for hardness rather than fight it; the remineralise calculator and my note on the ideal GH for shrimp both go into that. On hard tap water you have nothing to do. That is the whole appeal of the site’s niche, really: for once the water is a feature.

The one genuine hard-water caution is not the shrimp, it is the moult. In mineral-rich water shrimp can occasionally struggle if there is a mismatch between GH and KH, or after a big water change swings the parameters. I change less water at a time in the shrimp tanks, around 20 percent, and match the new water’s temperature, and I have not lost a shrimp to a failed moult in a long time.

The book behind Lagonia

The Hard Water Aquarium

My practical guide to working with hard, alkaline tap water instead of fighting it: reading your water, choosing and setting up the tank, and keeping and breeding the fish that thrive in it, from livebearers to Rift Lake cichlids and shell-dwellers.

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What they eat, and what they will not touch

Amanos are the best all-round algae grazers I have used, but “algae eater” oversells it if you expect a spotless tank. Here is the honest breakdown from my tanks.

They reliably clear soft green hair algae, thread algae and the fuzzy biofilm that coats new hardscape and slow-growing plants. Drop a group into a tank with a hair algae problem and you will see real progress within a fortnight. They also hoover up leftover food, dead plant matter and the odd dead snail, which makes them genuine cleanup crew rather than decoration.

They are hit and miss on black beard algae. You will read that they eat it, and hungry Amanos will sometimes graze the soft new growth, but I would never buy them to clear an established black beard outbreak. That is a water-flow and nutrient problem you fix at the source, and my algae guide covers the real causes. They also largely ignore the hard green spot algae on the glass; a nerite snail is the tool for that, and my snail piece explains which snails actually help.

The important management point: a hungry Amano is a working Amano. If you feed the tank heavily, they will loaf about eating fish pellets and ignore the algae, because given the choice they prefer the easy meal. In a tank kept as a cleanup crew I feed them almost nothing extra. If the algae runs low, I offer a little blanched courgette or spinach, or a calcium-rich shrimp pellet a couple of times a week, and no more. You will also see them eat their own shed shells after moulting, which is normal and worth leaving alone, since it recycles the minerals.

The breeding truth: you will not build a colony

This is the single biggest misunderstanding, and it is worth being blunt about because people waste months on it. Amano shrimp will not breed in a normal freshwater tank.

A female will carry eggs happily; you will see a green or brownish saddle of them under her tail. But the larvae that hatch are tiny, planktonic and helpless, and they need brackish or full salt water to survive their first weeks before they metamorphose into little shrimp and migrate back to fresh water. In a freshwater aquarium the larvae simply die within a few days. Breeding them at home means a separate brackish larval tank, careful salinity changes and live micro-algae to feed them, and it is a genuine project that most keepers, myself included, do not bother with.

So plan for it. If you keep cherry shrimp you get a colony that replaces itself for free. With Amanos you are keeping a fixed group that will slowly reduce over years, and you top it up by buying more. It is not a fault, it is just the deal, and it makes them safe to mix with other shrimp species since there is zero risk of hybridising.

How many, and in what size tank

For algae control I work on roughly one Amano per 8 to 10 litres as a starting point, then adjust. A 60 litre tank with a mild algae problem does nicely on five or six; if the tank is heavily planted and bright, err higher. Buy them as a group in the first place, because they are more relaxed and graze more openly in company.

They will live in a nano tank, but I prefer to give them a bit of room and a mature, planted tank with plenty of surfaces to graze. Two things matter for the setup. First, they are escape artists, and a determined Amano will climb the filter pipe and out through any gap, so a tight lid is not optional. I have found more than one dried out on the floor in my early days. Second, they need cover and something to grip while they moult, when they are soft and vulnerable for a day, so plants, wood and rock all help. Work out your real volume with the tank volume calculator before you decide on numbers, since the litres printed on the box are usually optimistic.

Tankmates: who eats whom

An adult Amano is too big for most small fish to swallow, which makes them harder to bully than tiny cherry shrimp. But “too big to eat” is not the same as “safe”, and freshly moulted shrimp are soft and defenceless.

Good company: small peaceful fish and snails. Tetras, danios, rasboras, Endlers and other small livebearers, Corydoras, and nerite or mystery snails all coexist with adult Amanos without trouble. In my own tanks they share space with livebearers happily.

Risky or plain wrong: anything with a mouth big enough and a taste for shrimp. Most cichlids will hunt them, and that includes the Tanganyikans this site is built around. My shell-dwellers would treat a moulting Amano as lunch, so I keep the two apart. Angelfish, larger gouramis, big barbs and anything goldfish-sized will pick them off over time. If you want shrimp in a cichlid tank, the honest answer is usually don’t; keep the shrimp in their own tank instead. To sanity-check any mix, my stocking calculator and the guide on how many fish you can keep will keep you from overloading the tank in the first place.

Are they worth it?

For a planted or hardscaped tank on hard water, absolutely. They are hardy, genuinely useful, undemanding once settled, and the very hardness that makes this hobby awkward for soft-water fish is a straightforward advantage for them. Just buy them for what they are: a hard-working, long-lived cleanup crew that you keep rather than breed. Give them cool, clean, hard water, a tight lid and not too much extra food, and they will quietly earn their keep for years.