Swordtail Tank Setup: A Real 29 to 30 Gallons and a Lid That Actually Seals

Swordtail Tank Setup: A Real 29 to 30 Gallons and a Lid That Actually Seals

Swordtails need more room than a guppy or molly, sturdier filtration to match, and a lid that actually seals, since this is a genuinely capable jumper, not just a hobbyist exaggeration. This covers the full setup, for what it all costs, see our Swordtail cost guide, or the full Swordtail care guide for everything else.

Tank Size

20 gallons is the genuine floor for a small trio, a step up from the 10-gallon tank that gets a small guppy or platy group by. But most direct retailers and care sheets for this exact species recommend going further: one major online fish retailer lists a 20-gallon minimum for standard swordtails, yet its own listing for the fancier Hi Fin Lyretail variety of the same species recommends an aquarium of at least 30 gallons that is well planted with plenty of room for swimming. That more generous number shows up consistently once you look past the bare minimum, since swordtails are noticeably more active, open-water swimmers than a molly or platy of similar size. Go long and rectangular rather than tall, and use a lid, more on that below.

A 20-gallon long tank is a workable starting point for a small trio, with a step up to 29 or 30 gallons the better real-world target for most keepers.

Temperature

A tropical range of roughly 64 to 82°F works, with 72 to 79°F cited most often as the steadier, more comfortable target. Stability matters more than hitting an exact number, avoid swings larger than about 2°F in a 24-hour period. A heater is necessary unless your room stays consistently warm year-round.

Water Chemistry

Swordtails do best with a pH of 7.0 to 8.4 and moderately hard to hard water, commonly cited as 12 to 30 dGH. If your tap water runs soft, a mineral supplement, crushed coral or a commercial buffering product, can bring it into range.

The Jumping Risk

This is worth its own section because it's genuinely one of the more consequence-heavy details in swordtail keeping, and it's real, not hobbyist exaggeration. One major retailer's listing for this species notes plainly that the tank requires adequate cover over the aquarium since these are jumpers, and hobbyist reports consistently describe fish escaping through gaps far smaller than you'd expect, a few inches at the back of a lid is often enough.

A full mesh or glass lid with no meaningful gaps is the fix, not an optional upgrade. Leave a feeding hatch or filter cutout no larger than necessary, and check it after any tank rearranging, since even a temporarily propped-open corner is enough.

Filtration

Swordtails need more real filtration capacity than a guppy or molly. SeriouslyFish specifically recommends filter flow at 4 to 5 times the tank's volume per hour for this species, and a bigger, more active fish in a bigger tank produces a bigger bioload to match. For a standard or growing group, a hang-on-back filter or a stronger canister filter handles the load comfortably.

If fry survival is the priority instead, a dedicated breeding or nursery tank, a gentle sponge filter is the better call, since it won't pull small fry into strong current the way a power filter can. Our Swordtail handling guide covers how that choice fits into a broader breeding or population plan, and however much filtration you land on, keeping portions in check matters just as much, our Swordtail feeding guide covers how much to actually drop in so the filter isn't fighting uneaten food.

Substrate

Fine gravel or sand both work well. Avoid sharp or coarse gravel, which can damage fins, especially on longer-finned lyretail and hi-fin varieties.

Lighting

A basic LED light on an 8 to 10 hour daily cycle is sufficient. It isn't strictly necessary for the fish's health, but it supports live plants and makes for better viewing.

Planting for Female Refuge

Dense live plants aren't just decoration in a swordtail tank, they're a genuine, practical tool for two separate problems. First, the same one covered in our Molly tank setup guide: swordtail parents don't look after fry, and adults will eat them given the chance, so dense live plants give fry somewhere to hide.

Second, and more specific to this species, planting gives females somewhere to physically break line of sight from a persistent male. Our Swordtail handling guide covers why male-to-female ratio matters so much here, and thick cover is the tank-setup half of managing that same problem, it doesn't replace a proper ratio, but it meaningfully softens the impact of one that's less than ideal.

The Non-Obvious Requirement: Cycling and Conditioning

Cycle the tank before adding fish. Building the beneficial bacteria colony that processes waste takes 2 to 4 weeks with a fishless cycle, or somewhat less with a bottled bacteria product. Skipping this step is one of the most common beginner mistakes in the hobby generally, and it's a fast route to the ammonia-driven stress covered in our Swordtail health issues guide.

Always use a water conditioner on tap water before it goes in the tank, dechlorinating and neutralizing chloramine and heavy metals that are otherwise harmful to fish. A water test kit lets you confirm the cycle actually finished and catch drift afterward.

Browse the rest of our Fish care guide category, or check the Swordtail encyclopedia profile for more.

Sources & Further Reading