Photo: Gonzalo Valenzuela · CC BY 2.0
Freshwater · Beginner · 15+ gal
Hemigrammus erythrozonus
By Fishy Dave
Glowlight tetras (Hemigrammus erythrozonus) grow to about 1.5 inches and carry a thin orange-red line from nose to tail. Keep six or more in a cycled 15-gallon, or eight to ten in a 20, at 74 to 82°F. Dark substrate, floating plants, and dim light make the line show.
| Water type | Freshwater |
|---|---|
| Care level | Beginner |
| Minimum tank | 15 gallons |
| Temperament | Peaceful schooler that stays in the middle and lower half of the tank. Keep six at the very least, and eight or more if you have the room. A small group hides and loses color. They leave plants, shrimp adults, and long fins alone. |
| Diet | Omnivore with a small mouth. Micro pellets or crushed flake once or twice a day, plus frozen baby brine, daphnia, or cyclops a few times a week. Feed what the school finishes in about two minutes. |
| Temperature | 74–82 °F |
| pH | 6–7.5 |
| Hardness / salinity | Soft to moderately hard, up to about 15 dGH. Farm-raised fish settle into most tap water if it stays steady. |
In a bright, bare shop tank, glowlights look like see-through minnows with a faint pink line. I have watched people walk right past them on the way to the neons. Put the same fish over dark sand under a few floating plants and that line turns into a glowing orange filament.
Hemigrammus erythrozonus comes from the Essequibo River basin in Guyana, but the fish you buy were bred on farms. Adults reach about 1.5 inches and can live around five years. The body is clear to silvery. An orange-red stripe runs from the snout, through the eye, to the base of the tail, and the top of the eye is red as well. The front of the dorsal fin is red, and the dorsal, anal, and pelvic fins have small white tips. Females are rounder through the belly.
Two other fish share the name. The glowlight rasbora (Trigonostigma hengeli) has a dark wedge on its side under the orange line, like a small harlequin. An ember tetra is orange all over and smaller. If the fish in the bag has a clear body with one bright line, it is a glowlight tetra.
Six glowlights fit a cycled 15-gallon. Eight to ten in a 20-gallon is where they start to swim as a school, and a 20 long gives them more front-to-back room than a 20 high. A 10-gallon is too small for a proper group. Wait until the cycle is done before you buy, because a young tank is hard on any tetra. How to cycle a fish tank walks through it.
Keep the heater around 76 to 78°F. They take 74 to 82°F, pH 6.0 to 7.5, and soft to moderately hard water, so most tap water works as long as it stays steady from week to week. That makes them easier to keep healthy than neon tetras in hard tap water. You don't need to chase low pH.
Light and decor matter more for this fish than water chemistry. Use dark sand or gravel, add floating plants or tall stems along the back, and pick a modest light. Moderate flow from a sponge filter or a turned-down hang-on-back is plenty. A lid is worth having, since a startled tetra can clear the rim.
Their mouths are small. Micro pellets or crushed flake make a good daily food, and frozen baby brine or daphnia a few times a week fills them out. Feed a little at a time so food doesn't sink into the gravel and rot. The feeding guide explains the two-minute rule.
Pick tank mates that are calm and small. Harlequin rasboras, ember tetras, pygmy or peppered cories, otocinclus, and adult shrimp all mix well. A honey gourami makes a good centerpiece in a 20, and a pearl gourami works in a 29. Glowlights can share a tank with neon or black neon tetras if each species has its own group of six or more. Eight glowlights, a honey gourami, and six pygmy cories in a planted 20 sits comfortably inside the stocking calculator's waste budget.
Glowlights often look washed out in the shop and for their first week at home, so wait a week or two before you judge the color. Float the bag to match temperature and net them in. See how to acclimate new fish. If you run a quarantine tank, use it. Neon tetra disease can hit glowlights too, and there is no dependable cure.
A few listings we would open for this species. Skip anything you already own that still works.
Hikari Tropical Micro Pellets, 0.77 oz
Small, slow-sinking pellets sized for a 1.5-inch tetra, so the school eats in midwater instead of chasing flake across the surface.
A pinch is enough for eight fish. Skip it if your current flake gets eaten before it hits the bottom.
See this listingAqueon Pro adjustable heater, 100W
Keeps a 20-gallon at 76 to 78°F in a normal room, the middle of the range glowlights like.
A 15-gallon is fine on a 50W heater. Check it against a separate thermometer rather than trusting the dial.
See this listingPAIZOO stick-on digital thermometer
Shows the real water temperature at a glance, so you know the heater is holding the tank inside 74 to 82°F.
Stick it on the end of the tank away from the heater. Skip it if you already have a thermometer you trust.
See this listingSix at minimum. Eight to ten in a 20-gallon is better. A bigger group swims more openly and shows more color.
Fifteen gallons for a group of six, and 20 gallons for eight to ten. A 10-gallon is too small for a proper school.
Usually it's bright light, a pale substrate, a new tank, or a group that is too small. Dark sand, floating plants, and a few more of their own kind bring the stripe back. If the color fades and the fish stops eating, test the water.
Yes. Once the tank is cycled they handle a wider range of tap water than neons or cardinals, and they are peaceful with almost any small community fish.
No. The glowlight rasbora (Trigonostigma hengeli) is a small relative of the harlequin rasbora with a dark wedge on its side. The glowlight tetra has a clear body with a single orange-red line.
Next step
Plan on 15 gallons or more. Put your actual tank size into the stocking calculator and it shows what else can live alongside them.
Open the stocking calculatorBefore you buy
Keep your fishies swimming.
Freshwater · Beginner
Paracheirodon innesi
Keep neon tetras in a school of at least 6, and plan on 8 to 12 in a 20-gallon tank. Adults stay under 1.5 inches. A 10-gallon is the minimum for a small school. Hold the water at 72 to 78°F, soft and slightly acidic (pH 5.5 to 7.0), with plants and dim light.
Min. tank: 10 gal
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Hyphessobrycon herbertaxelrodi
Black neon tetras (Hyphessobrycon herbertaxelrodi) stay about 1.5 inches. Keep at least six in a cycled 15-gallon, or eight to ten in a 20, with plants, moderate flow, and water at 72 to 80°F. They handle ordinary tap water better than neons or cardinals do.
Min. tank: 15 gal
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Hyphessobrycon amandae
Ember tetras (Hyphessobrycon amandae) are ~0.7-1 inch orange nano schoolers for a planted 10-20 gallon. Keep 10 or more with gentle flow, plants, and micro foods. A 10-gallon works for a species school; use 20 gallons if you mix in other fish.
Min. tank: 10 gal
Care notes →
