How Many Glofish Are Actually Recommended Per Gallon?

First of all, let me point out that the “inch per gallon” rule does not apply for Glofish. Moreover, that rule is not and will never be correct for any species of fish. Imagine putting a 10-inch fish in a 20-inch (10 gallons) tank. With good filtration, It will probably survive, true, but will it be happy? Probably not. One of my personal rules on the matter is that this is not a hobby, these are our pets. We need to treat them with love and care. They deserve to be happy. But I digress. Let’s dive right in.

Exactly how many Glofish will be alright in a gallon of water?

There are a couple of things you need to know about Glofish before we proceed:

1. Glofish are schooling fish – they need the comfort of living in a group and swimming in a group.
2. Glofish are not one species of fish – there are many genetically modified fish that end up glowy. Most popular ones are the Black Skirt Tetra and the Zebra Danio.

That being said, here’s how many Glofish is accepted for one to keep per gallon of water:

Glofish thrive in a group so it is recommended to have at least 5 from the same species. If you plan on getting 5 to 6 Glofish then a 20-gallon tank will be suitable. Keeping them in 3, 5 or 10 gallons of water will result in poor life quality and aggression. For a 9 to 10 Glofish tank, it’s advisable to provide 30 gallons of water for living space.

Get the long tank and mind decoration

These species are highly active and like to swim around a lot. You’d need 3 gallons of water per Glowfish at the minimum.

This leaves a 10-gallon tank (and everything below that) out of question.

Keep in mind that decorations take up space and reduce the overall water, available for fish. Sticking a considerably large piece of driftwood in your tank can be beautiful but it will reduce the swimming space even further. Click the link if you want to learn where to find the perfect piece for your aquarium, by the way.

You’d also want to take into consideration that the glowing Danios like to speed around in your aquarium and need more horizontal space. If they are your Glofish of choice you’d want to have a long fish tank.

Tetras are quite active (and attractive) swimmers as well.

If you plan to get the bare minimum and don’t own other fish a 10-gallon tank won’t be enough. From my personal experience, it is always best to scale up things by a level. I always liked to keep my tanks stocked at 70 to 80% population. This way my fish would reach their full potential and not feel confined in any way. If you do, by any chance, plan to add tank mates to your Glofish aquarium setup you will have to get a bigger tank eventually.

Recommended read: Top Fish to Stock a Small Tank

Why do Glofish need to be in groups?

Most Tetras and all Danios should live among their brothers.

The Zebra Dario and the Skirt Black Tetra are both schooling fish species. This means that they will coordinate their swimming and do it in the same direction.

Which is, in my opinion, the perfect view from a fishkeeper’s perspective.

Glo tetras and Glo tiger barbs are known to become aggressive when not in schools. If you keep too few of the same species they will feel lonely and may even die earlier.

These are social species.

I’d encourage anyone who’s excited about having an aquarium to have at least a couple of those. They make the aquarium feel alive and, dare I say, are more entertaining to observe than most TV dramas.

A couple of friendly reminders about keeping Glofish for our fellow beginners

Here are a few tips for proper Glofish care to consider before starting a glo-tank:

• They are tropical – A heater is a must and so is a thermometer. Keep a water temperature of around 78°F (25.5°C). The link leads to one I like myself, but you can skim this page and find what suits you best.
• Proper cycling – You’d need to cycle your tank for a month before adding ANY fish to it. There are faster ways to do that if you are impatient though (click the link to read my guide on using bottled bacteria). Tetra SafeStart Plus is my go-to brand of bacteria starter for cycling new aquariums. My advice here is to add 2 to 3 fish every 12 to 15 days AFTER the tank has been cycled. This way you will not overload your beneficial bacteria with ammonia. Use very little fish food during the cycling process to feed the bacteria.
• Get the long tank – Active swimmers need the distance. Another benefit is that it will be really fun to watch them dash through your tank.