My son is going to get an aquarium.

We picked out a 20-gallon, long aquarium (along with some plants and decorations). I have yet to pick substrate, pump/filter, etc.

I'll be setting it up and taking care of it until he is old enough and responsible enough to maintain it on his own, but we've let him pick out what will go in it.


  • neon tetras
  • fancy guppies
  • cherry barbs
  • golden barbs


  • African claw frogs
  • apple snails (for cleaning)

Considering the size of the aquarium, how many of each of the above creatures should I get to start? Are there general guidelines for starting populations?

It has been many, many years since I've kept an aquarium. I'm assuming I want more than one of each, since they're all small. I also recall that the guppies I had as a kid tended to breed pretty fast.

Are there ideal numbers I should shoot for for each creature, in order to keep the fish happy and healthy? This answer seems to indicate I'll be looking at a maximum of between 10 and 20 total fish (assuming I remember the size of the 4 fish species I listed correctly), but is there a minimum?

Do some of these species do better in larger numbers, and others in smaller groups? Should I start out at small numbers to account for population increase due to breeding?

  • 2
    I must admit I'm confused by the "primarily opinion based" close vote. I'm looking for information about the specific breeds, and what the initial population of each should be in order to keep the overall populations manageable and healthy. I'm not asking "what is most aesthetically pleasing". If the question could be improved, I'd appreciate feedback, and would be happy to clarify, but I could use some guidance as to where the confusion lies. – Beofett Apr 7 '14 at 17:29

You'll always want to add fish into a tank slowly. When you add fish in, there's going to be a bit of an ammonia spike as the bacteria in the tank processes the chemical imbalance. The trick is balancing out how many fish you can add that won't cause too much of a chemical imbalance that they'll be harmed by it. That's why I usually suggest adding the hardiest and smallest fish in first.

The smallest fish in your case would be the neon tetras. They usually only reach about 1.5 inches in length when full grown. But, they are also quite sensitive to changes in the water (temperature and chemicals). So in that case, I'd suggest adding the guppies first, as they only get about 1.5-2 inches in length and are quite hardy fish.

The fish you've chosen are all considered schooling fish, so in order for them to feel comfortable in the tank you'll want to make sure that they have enough of their own kind in the tank with them. In general, 4-5 fish are the minimum needed for a small school. Although there are other factors to consider.

  • The neon tetras, they'll start to shoal once you get about 8-10 of them together.

  • Barbs are typically more aggressive, so by overstocking the tank a bit, you remove the territory that they can claim as their own, making them less likely to pick on other fish. Cherry and golden barbs aren't quite as aggressive as far as barbs go, but you might want to plan on a bit more of them than the others.

So as far as numbers go, I would put about 4-5 neon tetras and guppies in, and 5-6 cherry and golden barbs in. When introducing them into the tank, I would add a new species in every few days.

I would only put one snail in for the sake of the snails reproducing on their own (you might end up with more than you bargained for in the end), and as long as you get the dwarf african frogs you can get a couple without too much worry about space since they just chill at the bottom of the tank for the most part. Just note that they produce a lot of waste you'll have to clean. Make sure they're not the regular african clawed frogs, as those get to be large enough that they would eat all your fish (think small bullfrog).

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  • Thanks! What do you mean by overstocking the tank to make the barbs more timid? I'm guessing you mean increasing the number of the other species present, compared to the number of barbs, but I'd like to be certain I understand properly. – Beofett Apr 8 '14 at 15:42
  • I made a Q&A for it, I had a bit too much for a comment. pets.stackexchange.com/questions/2835/… – Spidercat Apr 8 '14 at 16:23
  • I was under the impression that barbs' tendency toward fin-nipping wasn't really about territory, but about social behaviour. Once they have a large enough group of their own kind, they tend to stop harassing the other fish. I thought that overstocking to eliminate territorial lines was more applicable to cichlids than barbs. – symbol Apr 10 '14 at 20:37
  • @symbol Part of it is social (I mentioned it in the Q&A I made), but most, if not all, fish will claim a fish tank as their territory. I've seen mollies divide themselves into groups of the ones who were there first, and the ones who were added a couple days later. – Spidercat Apr 11 '14 at 2:02

Stocking is very subjective to the specific inhabitants as well as the setup and your aquarium experience. There's a general 1" of fish per gallon guideline for FW tanks, but that's also subjective and most experienced aquarists disagree with it. For your size fish it should be mostly appropriate.

Since you're just starting out with it, I would get the tank setup with substrate and water and filter and let it go through the initial cycle which takes about 30 days. Until the cycle is complete, the tank isn't fit for any inhabitants.

As far as recommendations on stocking, the tetras do better in a school, 6 - 10 or more is ideal. The barbs usually appreciate at least a few of their own kind as do the guppies. The barbs are also prone to fin nipping which the guppies would be most susceptible to. I would be hesitant with those snails as they can and will reproduce and can get out of control. Nerits are a better match as they devour most types of algae and they cannot reproduce in fresh water. Clawed frogs are typically fine but the are rather messy and require a lot more food than fish to remain healthy.

As far as breeding goes, it's not going to be an issue. Even if some do successfully reproduce, there is zero change the babies will survive in a community style fishtank. The guppies are the only ones that will readily reproduce. You could use a net breeder if you wanted to try and rear some of the fry to adulthood.

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  • Merely setting up the tank and filter and letting it run won't cycle it on its own. The cycle won't start until there's a source of ammonia, either from fish or by being added directly or from food being broken down. If you were to set up the tank and put a bit of food in every day as if it had fish in it, it would likely be cycled after a month (test the water to be sure), but the nitrogen cycle cannot start without a source of nitrogen! – symbol Apr 10 '14 at 19:34

If you'd just like the final numbers and are less concerned about the reasoning behind them, answer is as follows: EITHER get 2 African clawed frogs OR 6 neon tetras, 6 cherry barbs, 6 gold barbs, 3 guppies, and 0-1 snails.

Detailed answer below:

African clawed frogs are generally recommended to be kept in a species-only tank. (As in no fish, just frogs.) Just so you know, African clawed frogs will eat guppies and probably most of the other fish as well. The guppies will likely breed if given half a chance, so this could be desirable, but I would count on the tetras and barbs getting wiped out as soon as the frog is big enough to swallow them. If your son (or you) would be upset by seeing his fish being eaten by his frog, then I would strongly recommend getting either frogs OR fish and not both.

Also select your substrate carefully. There's a good chance that the frog will ingest some of it at some point and if the substrate is too large or sharp it could do severe (potentially fatal) damage to the frog's digestive tract. Either select a substrate that will be too large for the adult frog to fit in its mouth or small enough and smooth enough that it will have a chance of passing through the digestive tract without doing damage. Pool filter sand would likely be safe for the frog but could potentially clog your filter. (I use pool filter sand in my tank and haven't had any issues, but I also don't have a frog kicking it up into the water column so your mileage may vary.)

Apple/mystery snails can get fairly large and have a pretty high bio-load, so just be aware of that. They may end up putting nitrates into the water (which will feed algal growth) faster than they can eat the algae when they get large. Also, like the substrate, they could pose a hazard to the frog if they get swallowed at an awkward size. And, if you get more than one apple snail, you may find yourself with a snail population explosion. Again, this could be desirable, but then again, it may not.

Tetras generally do best in groups of at least six. (Speaking from experience, I can say that I say a dramatic change in behaviour when I went from four black neons to eight.)

Guppies are generally best kept in ratios of at least two females to one male. (Unless you don't want them breeding in which case you might want to consider all females.)

Barbs should generally be kept in groups of at least six. They may fin-nip the guppies, especially if you end up with a variety with particularly long fins (veiltails). Keeping them in larger groups (12+) generally reduces fin-nipping. However, I wouldn't recommend putting that many fish in a tank this size.

Even with the minimum recommended numbers of each species (6 of each type of barb, 6 tetras, 3 guppies, 1 frog, 1 snail) and a good filter, you'd likely be looking at doing 50% water changes twice a week.

If your son is more interested in the frogs, then you could quite happily house a pair of African clawed frogs in a tank that size.

If he is more interested in fish, then you could put all four of those fish species together in that tank (6 cherry barbs, 6 gold barbs, 6 neon tetras, 3 guppies). However, I'd still recommend that you keep a pretty close eye on water parameters (weekly testing) and consider doing at least a weekly 50% water change.

If there's one particular fish that your son would like more of, then maybe you could discuss going with only three species instead of four to allow for more of whichever one he's most interested in. (All of the fish you mentioned would also do well in larger groups.)

If you do decide to get both male and female guppies, try to come up with a plan for what you will do with the surviving fry. (Some may get eaten or sucked into the filter, but some will more than likely survive.)

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