While some beginners use a 5-gallon tank for platyfish, I highly recommend that a 10-gallon tank is an ideal minimum you can go for. But how many platies should you stock in such an aquarium, considering you have to add some plants to provide hiding places in there?
It is recommended to keep a maximum of 6 platies in a 10-gallon tank while maintaining a ratio of 2 females for 1 male. Therefore, a 10-gallon tank is enough for 4 female and 2 male platyfish. Remove any fry from the tank soon enough to prevent overcrowding and aggression.
| Tank size | Male and female platyfish |
| 5 gallons | 2 females, 1 male |
| 10 gallons | 4 females 2 males |
| 20 gallons | 8 females, 1 male |
| 30 gallons | 14 females, 7 males |
| 40 gallons | 18 females, 9 males |
The number of platies to keep in an aquarium depends on their behavior and size. A tank can support more platy fry than adult platies because the competition for food and space in the aquarium is immense among adult platyfish than in fry.
Platy fish are easy to care for because they don’t need much attention. In a 10-gallon tank, have at least one male platyfish for every three females. If you do that, your platies will breed in a short period.
How many platies to keep in a 10-gallon tank?
An adult platy fish requires about 2 gallons of fresh water to thrive and remain happy. Depending on the size of the fish, stock 5-6 platyfish in a 10-gallon tank.
If you choose to keep both males and females, expect a little aggression because the males will always try to mate with the females.
Being livebearers, platies will soon give birth to fry in the aquarium, which can lead to overpopulation and heightened competition for food. I’ve seen female platyfish hunt and eat their fry when enclosed in a small tank.
You want to remove the fry as soon as possible to prevent them from being eaten.
Alternatively, keep all female platies in such a small aquarium instead of encouraging breeding. You can also keep same-sized male platies to prevent them from harassing each other.
Here is a summary of the ideal number of platies for various tank sizes:
| Tank size | Ideal number of platies |
| 5 gallons | 3 |
| 10 gallons | 6 |
| 20 gallons | 12 |
| 30 gallons | 21 |
| 40 gallons | 27 |
Pro tip: Supplement your platy fish diet with omega-one flakes or pellets, brine shrimp, and bloodworms to keep them healthy in a small tank.
Water chemistry in a 10-gallon platy tank
A ten-gallon tank does not provide enough room for variety and the social needs of platyfish. Keep the water stable and within the ideal parameters for your platies. Under normal conditions, change 25% of the water every two to four weeks.
I recommend adding only three platyfish at once. Adding too many platies to the tank at once could destabilize the water chemistry and stall the nitrogen cycle. Putting many platies at once can alter the pH levels of the water and sicken or kill your fish.
It takes between six and eight weeks for platyfish to give birth. And they can give birth to eight or as many as 40 fries at once. Unless you are breeding the platies, ensure that males are more than the females in the ratio of 2:1. Otherwise, more females than male platies would dramatically increase their numbers in the tank.
A bigger tank is essential for protecting the fry from hungry adult platies. For example, a 40-gallon tank gives the fries adequate space to hide and flourish. I would recommend it if you’re planning on breeding your platies.
A larger tank means happy platies since water chemistry and temperature are more stable than a more miniature ecosystem. See also my guide on temperature tolerance in platyfish.
How many platies with tank mates in a 10-gallon tank?
Platyfish are easy-to-care-for and add to a community tank if it is big enough. However, platyfish prefer the company of their own kind. If you want to add new tank mates to live with platies, do it cautiously and observe their behavior for a while to determine if they are compatible.
It can make your platies shy and anxious. But if you want to, then prioritize mates with peaceful demeanors over aggressive species.
Here are some platyfish tank mates I’d recommend introducing in a small tank:
- Cardinal Tetra
- Celestial Pearl Diano
- Cory catfish
- Guppies
- Molly Fish
- Rainbowfish
- Swordtail
You can, however, try keeping different varieties of platyfish instead of introducing other species in the same tank. I find fixing water chemistry in a multi-species aquarium quite demanding.
Considerations
Several vital factors determine the number of platies you can keep in a tank at a go. To decide the best tank size, consider the size and number of the platyfish, their activity level, social behavior, and the number of hiding spots.
Also, note that platies enjoy schooling and keeping them in groups is an added advantage. Here is an in-depth look at those considerations when determining the number of platies to keep in your aquarium:
Size and number of platies
Platies grow to about three inches. The fish are so small that it is easy to overcrowd them in a tank. However, do not be deceived by their size because adult platies require significant space to remain happy.
The rule of thumb is that the more the platies you add, the bigger the tank you need.
Platy fish activity level
Platies are highly active. They explore the middle and top parts of the tank and hide among plants. The fish are nonviolent but have a ravenous appetite. Overcrowding them in a tank could create significant competition and stress for the fish beyond what they can endure.
To prevent aggression, balance females to males at a ratio of 2:1.
Platy’s social behavior
It is also essential to consider the social behavior of platyfish. Peaceful and friendly fish like platies enjoy living in groups. That means you should not keep one platyfish in a tank.
As I said before, grouping the fish in multiples of three to six is ideal. The smallest number of platies to keep is three. That means you need a tank that is at least five gallons.
The number of hiding spots
Create hiding spots for platyfish using aquarium plants, rocks, and ornaments such as pipe ornaments.
It is challenging to create many hiding crevices in small tanks because the materials themselves consume significant space in the tank. If you have many platies, say 30, you’d need more hiding spots for the fish in a 30-gallon tank.
As such, you want to consider a larger tank with more hiding spots in the tank.
Platy’s feeding habits
Various fish species have different feeding habits. Platies, for instance, are omnivores with broad nutrition. They can feed on algae, plants, and small crustaceans like brine shrimp. Feed the juveniles two or three times a day and the adult platies only once a day
A larger tank is appropriate to reduce the concentration of fish poop that may cause ammonia poisoning and stress.
Problems with overcrowding platies in a small tank
An overcrowded fish tank can lead to severe problems for your platies. For example, more than ten platies in a ten-gallon tank can make the fish aggressive, overly territorial and nip each other’s fins.
That could cause stress and infections that could spread in a closed environment like an aquarium.
Too many platies can also overload the tank with lethal levels of toxic fish waste. The major problems with overcrowding platies in a small tank are ammonia poisoning, stunted growth, foul-smelling water, and discolored water.
Ammonia poisoning
The ideal water tank for your platies should not have ammonia. You will know your platies have ammonia poisoning if you notice purple or red gills or symptoms such as gasping for air at the tank’s surface. Ammonia poisoning occurs when the pH rises and offsets the nitrogen cycle due to algae activity and the accumulation of platyfish waste.
Foul-smelling water
Although bad-smelling water is attributed to excess fish waste and food, overcrowding also causes it. If you have many platies in a small tank, the chances are that you drop lots of food and the fish poop more often. Avoid changing the water at once. Change 50% of the bad-smelling water and 25% the next day.
Stunted growth
Overcrowding also causes stress and competition for food and resources for platies in a small tank. Stress lowers the immunity of the platies, but it also stunts their growth. Feed your fish adequately and increase the size of the tank or reduce the number of the platies to promote healthy growth and lifespan of your platies.
Discolored water
Overcrowded platies eat a lot, reproduce a lot, and excrete a lot. It also results in significant competition and overfeeding. Disturbing the chemistry and nitrogen cycle promotes algae and causes cloudy or green water. Cut back on feeding your platies and change 50% of the water.
References
- Hamilton, T. R. (1981). Platyfish: Versatile Animals for the Laboratory and Classroom. The American Biology Teacher, 426-472.
- Hill, J. E., & Yanong, R. P. (2002). Freshwater ornamental fish commonly cultured in Florida. Circular 54, Institute of Food and Agriculture Sciences, University of Florida, USA, 6.
