Marc Dobler | Web Developer, DIY Maker

Marc Dobler

Fish for 20G Nano Reefs


The purpose of this thread is to provide you with a comprehensive guide to fish for the nano reef aquarium.

As for reefing, in general, is not an exact science the approach, I have taken to organizing this information is to provide a framework that includes my knowledge and experience with nano fish both as a hobbyist and professionally but also to encourage others to share their experience and knowledge for the benefit of everyone.

Your responsibility as a fish owner

Fish are living things and deserve to be cared for as you would any other animal. Their life and well-being should not be valued by their price or just because they are easy to replace.

As a fish owner, you should strive to give your fish the most natural life possible, respecting that you have removed this animal from its natural environment.

To be straightforward, if you aren't willing to put forth the effort, time, money, and do the necessary research to properly take care of and create the ideal environment for your fish, you need to find a different hobby.

Words of wisdom

  • Design your aquarium around what fish you would like to inhabit it with. Never expect a fish to just adapt to a less than adequate tank size.
  • Plan your aquarium around the maximum size the fish will get. Just because it is a baby does not give you an excuse to keep it in a smaller tank.
  • Regardless of what the fish guy at Walmart told you, fish do not only grow to the size of the tank you put them in.
  • Fish stores are businesses and looking to make money. Some great fish stores really do care about their customers, their customer's tanks, and give out great advice. Unfortunately, that is not as often the case as it should be. Exercise extreme caution when taking advice from fish stores until you know they are really interested in helping you have an amazing tank and not just taking your money.
  • Research, research, and more research! Learn everything you can!

How to use this guide

Basic overview

There are four major sections in this guide: feeding, compatibility (coming soon), fish suggestions by tank size, and fish suggestions by a group. The feeding section allows you to get feeding suggestions based on diet type (carnivore, herbivore, omnivore, etc.) and more specifically by fish group, which includes more detailed info.

The compatibility section will most likely be in the form of a table in which you will be able to see how the species interact with other fish species, corals, and invertebrates.

In the fish, by tank size section a list of appropriate fish will follow each of the major divisions of tank sizes, as well, include a brief estimation of how many fish would be appropriate for that tank size. In the fish by group section, more detailed information will be provided about the major group each fish belongs to with some specific notes about each fish when necessary.

You will also see an estimated maximum size the fish will grow to and the ideal tank size. The ideal tank size will be a compromise based on what is socially practiced by many nano-reefers and what is often recommended by experts. Some of these ideal tank sizes may be controversial and if you believe so, you are welcome to bring that up in this thread so we can all as a community discuss it.

Things to keep in mind

  • Some of this will surely be my opinion or the opinion of others. If you feel strongly against something I have said, please pm me so we can discuss it and make changes if necessary.
  • This is just to get you started--ultimately you need to do more research on your fish choice before buying
  • Also, keep in mind I may list some things that are pushing it. I don’t know whether you are a beginner or expert if you know how to do a water change or not, so I will assume anyone who uses this guide has some common sense and basic understanding of nano reefing. For example, the fact that I list some fish appropriate for a 0.5g and 2.5g tank, does not automatically mean you should keep a fish in a tank that size. Rather, it means if you are capable of maintaining the added bioload of keeping a fish in a tank that size, then these fish would be appropriate choices.
  • Don’t forget to keep your bioload in mind. While a dwarf lionfish may only get 4-6”, due to their diet, the contribution to the bioload of your tank will be much more significant.

How you can contribute to this thread

Again, I would like to strongly encourage everyone to share his or her knowledge and experience. Please feel free to suggest additions, corrections, or other changes.

Also, I've tried to make a note when a species is available captive-bred, so if you learn of a new species that is available, let me know!

General feeding info

General thoughts

Meeting the nutritional needs of your fish is absolutely essential to their growth, survival, and reproduction. When feeding fish, we are trying to replicate not only what a fish eats, but when and how it eats in nature. The feeding preference of fish typically falls into one of five categories: carnivores, who eat meaty foods; herbivores, who eat plant matter; omnivores, who eat both meat and plants; piscivores, who eat other fish; and finally omnivores (detrivores), who obtain their energy from eating the animal and plant matter found within detritus.

You can get a good idea of what to feed your fish just by figuring out what feeding category your fish falls into. It's important to remember that not only can you starve your fish, but you can actually overfeed them too, both of which can have negative health consequences.

Fish are opportunistic eaters, meaning they never know when they will get their next meal, so eat whenever food is available. You may notice your fish eats anytime you put food in the aquarium, but that doesn't mean they are hungry, rather just taking advantage of an opportunity.

While you need to feed your fish, you also need to limit feeding too.

Overfeeding usually has drastic consequences on water quality anyways, so why would you want to put food in your tank if you don't have to. There are a few different types of food commonly available: live, flake/pellet / freeze-dried, frozen, and some hobbyists feed fresh meats and/or vegetable/algae.

To keep things simple I am mostly going to stick with what the average reefer is feeding, which is usually a commercially prepared flake/pellet and/or commercially frozen foods. I am revisiting this topic later at some point to include live and fresh foods, but I won't really get into that right now.

A few things to keep in mind

  • The more variety the better...keep multiple types of food and switch things up frequently. Feed a general staple food such as plain frozen brine shrimp or a general omnivore flake food (such as ocean nutrition formula one) and then supplement that with a variety of other frozen, flake, fresh, and live foods.
  • Stick with high-quality foods that are low in moisture, ash, and high in vitamins and nutrients.
  • Use or mix in foods that are enhanced with HUFA, omega-3 fatty acids, and vitamin C. Liquid supplements are also available that can be added to any type of food.
  • Do not overfeed!
  • Again, I will provide you with suggestions, but ultimately it is up to you to research the nutritional requirements of your fish.

Note: In making my suggestions I will refer to foods specifically made by Ocean Nutrition, H2O Life, and San Fransisco Bay Brand, given these are the brands I use and have the most experience with. There are many other high-quality manufactures of fish food though and those manufactures often have comparable products that you could use in place of the brands I mention if you wish.

Feeding schedule

There really isn't a great well-summarizing answer to how often or how much you should feed your fish with a lot of what you hear being based on experience and/or opinion. Some people feed once a day, some feed every other day, and others feed small amounts several times a day. I don't think one way is right over the other, but for simplicity, will suggest a small amount once or twice a day.

You want to try to incorporate in as much variety as you can. If you feed once a day, feed something different, or switch back and forth every day. If you feed twice a day, perhaps try frozen at the first feeding and flake at the second. Again, with feeding twice a day I'd suggest your second feeding complement what you did with your first feeding.

For example, if in the morning you are fed a meaty high protein frozen food then use an algae/seaweed flake for the second feeding. The amount you feed...although I'm not a fan of rules of thumb, I think only feeding what your fish can fully eat in about 5 minutes is a good place to start.

If it is all gone before 5 min, perhaps add a little more. If there is a lot of extra food flying around after 5 min, obviously you need to cut back. Any extra uneaten food will harm your water quality. Have a good sharp knife too because most likely you will be using fractions of frozen cubes, not the whole cube.

For that reason, it can be easier to use frozen flat packs which make it easier to break off only what you need, if the frozen food type you want is available that way.

How to use the feeding suggestion guide

There are two different ways you can use the feeding guide. I will provide feeding suggestions based on if the fish is a carnivore, herbivore, omnivore, piscivore, or detrivore and I will also provide feeding suggestions for each specific group of fish, noting species that do not follow trends of the group as a whole or have additional special needs.

To save time, so I don't have to repeat myself, I'm going to make a list of the common foods by the manufacture, and then will refer to those foods by number in both sections of the guide.

Food list by the manufacture

  • Ocean Nutrition

    • Frozen:

      1. Formula 1
      2. Formula 2
      3. Brine Shrimp Plus
      4. Brine Shrimp Plus w/ HUFA
      5. Prime Reef
      6. Angel Formula
      7. Spirulina Formula
      8. Pygmy Angel Formula
    • Flake/Other:
      9. Formula 1
      10. Formula 2
      11. Prime Reef
      12. Nano Formula

    • Dry Seaweed:
      13. Green/Brown/Red Algae/Seaweed

  • H2O Life

    • Frozen:
      14. Brine Shrimp
      15. Mysis Shrimp
      16. Cyclops
      17. Spirulina/Brine Shrimp/Mysis Special Mix
      18. Marine Fusion
      19. Silversides IQF
      20. Fresh Krill

    • Dry Seaweed:
      21. Green/Brown Seaweed

  • San Fransisco Bay Brand

    • Frozen:
      22. Brine Shrimp
      23. Spirulina Enhanced Brine Shrimp
      24. Marine Cuisine
      25. Omega Brine
      26. Angel and Butterfly
      27. Emerald Entrée
      28. Cyclops
      29. Reef Plankton
      30. Krill
      31. Silversides

Feeding suggestions by diet type

Carnivores: 1,3,4,5,6,9,11,14,15,18,19,20,22,24,25,26,30,31


  • Strictly Plant/Algae based: 2,7,10,13,21,27
  • Blends that include Plant/Algae which herbivores can feed on 1,8,9,12,17,23

Omnivores: They will basically eat most of what is listed above. I'd recommend using the blended frozen/flake mixes and/or alternating between carnivore and herbivore froze/flake formulas.

Piscivores: 19,20,30,31

Feeding suggestions by fish group

Coming soon!

Nano fish compatibility

Coming Soon!

Nano fish listed by tank size

Note: Suggestions for Seahorses by tank size can be found under the "Seahorse" heading in the next section of the guide, Nano Fish Listed By Group, for the time being.


  • B = Beginner (Ideal for first-time fish owners and or new tanks)
  • I = Intermediate (Ideal for hobbyists with established tanks)
  • D = Difficult (Ideal for experience hobbyists who can meet the special needs of these fish)
  • ** = Available Tank Raised (Please let me know if I am missing any)
  • V = Venomous

Note: There is a lot of controversy around the idea of keeping saltwater fish in tanks under 10g. Whether or not it is ethical will be up to you to decide and not something I'm going to get into. Like it or not, the fact is there are going to be people who do it. Therefore, I would rather at least provide those people with some guidance to make good choices instead of just leaving them in the dark.

Note Mandarins / Dragonets: There is a lot of controversy around the idea of keeping fish from the Dragonet family in nano tanks. Whether or not it is ethical will be for you to decide and not something I'm going to get into. I personally do not encourage people to keep dragonets in nano tanks, however, despite my feelings there a many who have successfully kept them in smaller tanks, therefore I will include them in this guide.

10G (38 L)

(1 - 2 fish)

Note: Keep in mind that the display area of all-in-one tanks holds less water than the total tank since some of that water is in the filtration area. When picking out fish, pick fish based on the display area volume, not the total tank volume.

  • Blue Neon Goby — Stiphodon atropurpureus **
  • Blue and Gold Blenny — Ecsenius lividanalis
  • Broadstripe Goby — Elacatinus prochilos
  • Catalina Goby — Lythrypnus dalli [cold water]
  • Citron Goby — Gobiodon citrinus
  • Clown Gobies — Gobiodon okinawae **
  • Clown Goby, Black — Gobiodon strangulatus
  • Court Jester Goby — Koumansetta rainfordi
  • Deepwater Candy Basslet — Liopropoma carmabi
  • Dracula Goby — Stonogobiops dracula
  • Gold Neon Eviota Goby — Eviota pellucida
  • Greenbanded Goby — Tigrigobius multifasciatus **
  • Longspine Cardinalfish — Zoramia leptacantha
  • Orange Spotted Goby — Amblyeleotris guttata
  • Orange Stripe Goby — Amblyeleotris randalli
  • Panda Goby — Paragobius lacunicolus
  • Pygmy Coral Croucher Goby — Caracanthus unipinna
  • Pinkbar Goby — Amblyeleotris aurora
  • Panamic Barnacle Blenny — Acanthemblemaria hancocki
  • Red Neon Eviota Goby — Eviota nigriventris
  • Red Sea Mimic Blenny — Ecsenius gravieri
  • Red Spotted Goby — Trimma rubromaculatus
  • Red Striped Goby — Trimma cana
  • Redhead Goby — Elacatinus puncticulatus **
  • Swissguard Basslet — Liopropoma rubre
  • Two Spot Goby — Signigobius biocellatus
  • Tail Spot Blenny — Ecsenius stigmatura
  • Trimma Goby — Trimma maiandros
  • Two Spot Bimaculatus Blenny — Ecsenius bimaculatus
  • Wheeler’s Shrimp Goby — Amblyeleotris wheeleri
  • White Spotted Dwarf Goby — Trimma cf. caesiura
  • Yasha White Ray Shrimp Goby — Stonogobiops yasha
  • Yellow Neon Goby — Elacatinus figaro **
  • Yellow Trimma Goby — Trimma kitrinum
  • Zebra Catalina Goby — Lythrypnus zebra D
  • Hi Fin Red Banded Goby — Stonogobiops nematodes
  • Hector's Goby — Koumansetta hectori
  • Jaguar Goby — Gobiopsis quinquecincta
  • Cave Transparent Goby — Fusigobius pallidus

15G (56 L)

  • Yellow Banded Possum Wrasse — Wetmorella nigropinnata D
  • Caribbean Deepwater Cave Basslet — Liopropoma mowbrayi D
  • Tanaka's Pygmy Wrasse — Wetmorella tanakai D
  • White Banded Possum Wrasse — Wetmorella albofasciata D
  • Pink-Streaked Wrasse — Pseudocheilinops ataenia D

20G (76 L)

(2 - 3 fish)

Note: Keep in mind that the display area of all-in-one tanks holds less water than the total tank since some of that water is in the filtration area. When picking out fish, pick fish based on the display area volume, not the total tank volume.

  • Comical Blenny — Ecsenius opsifrontalis
  • Ocellaris Clownfish (False Percula) — Amphiprion ocellaris B **
  • Percula Clownfish (True Percula)** (1, if you want a pair, move up to 20G) — Amphiprion percula B
  • Firefish Goby B — Nemateleotris magnifica
  • Red/Orange Angler — Antennarius sp.
  • Wartskin Angler — Antennarius maculatus
  • Painted frogfish — Antennarius pictus D
  • Firefish, Helfrichi — Nemateleotris helfrichi
  • Elegant firefish — Nemateleotris decora
  • Pajama Cardinalfish — Sphaeramia nematoptera
  • Exquisite Firefish — Nemateleotris exquisita

Nano fish listed by fish group

Coming Soon!



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