I've bought a few adult guppies around 9 months ago.

One of these guppies was gravid and gave birth around a few days after I got her.

I had kept the adult and the fry in the same container (simple glass tank without a filter, shown in the picture).

enter image description here

Now my concerns are as follows:

  1. It appears that some of them have not grown at all, it has been approximately 8-9 months!

  2. Is the mentioned container (considering it has no filter) okay to keep them in? Is getting a different tank with built in filter recommended?

And in general I'd like to ask if anyone has any tips raising guppies, since I've been reading up a lot but there was nothing said about their growth rate being so erratic.

  • 3
    How big are they now then? And guppies are known to breed very fast. Isn't it possible you simple see new offspring all the time? Also, it's a bit difficultto judge the size of that bowl, but that definitely seems way to small to keep fish in. Guppies will need at least around 60 litres, a filter and a heather in order to be happy. And since they breed very fast, you might even need a bigger tank quickly if you want to keep them.
    – Diether
    Commented Jul 6, 2017 at 10:41
  • 2
    I agree with Diether that the container is too small and with the recommendation of 60l. It's a miracle that the fish survived so far without filtration. How often do you change the water. The fry might die immediately because of toxines into the water which are present because of the lack of a filter. Commented Jul 6, 2017 at 11:52
  • 2
    The container is dominated by a giant (in comarison) platic plant. If this plant was not specifically made for fish tanks or made with food-safe plastics, it constantly releases toxins into the water.
    – Elmy
    Commented Aug 3, 2018 at 7:32

1 Answer 1


There are a couple of issues that I can see here that may be limiting how your fish grow.

1. Temperature

You didn't mention having a heater for the tank and I cannot see one in the picture that you have provided. Whilst guppies can survive in colder water, to make a fish thrive you want to provide all the chances you can.

A stable temperature is very important and warmer water around 25-28 °C (77-82 °F) tends to provide the best conditions

Source: Guppies and Mollies - thinkfish.co.uk

Even if you live in a climate that might allow the temperature to normally reside within this window, you'll probably want a heater for consistency.

2. Water Quality

Generally in my experience, a large volume of water is easier to keep at a higher quality because fluctuations caused by water changes have less impact on the aquarium's water quality parameters.

A filter is a must for a sustainable tank for a number of reasons. You'll want to check out the nitrogen cycle if you're not familiar with it already. To keep a tank sustainable for fish it must be 'cycled' so that you don't get a build up of toxic ammonia in your tank. If you haven't got yourself a water quality test kit you'll probably want to look into that too. The filter will also help to keep the water moving, agitating the surface, and allowing for more oxygen to dissolve in the water.

Ensure that you are doing regular water changes (normally between 15-25% a week) to keep the levels of nitrate down.

3. Aquarium Size

The tank you've got there looks pretty small. You should probably have at least 30 litres to give them a good enough space to live comfortably in. If you intend to bread them heavily, you'll need something much larger because they are prolific breeders.

As with most fish, the better you can set up their environment, the better they'll grow and the longer they'll live.

Closing Thoughts

This probably looks like a lot of information. Well, I guess it is. The key points here are:

  • Make sure the tank setup is suitable (size, temperature, water quality).
  • Consistency is key (It's widely agreed that chancing the perfect parameters does more harm than good in the long run. Get a good setup going and then maintain it).
  • Reach out! (The best thing you can do is to ask for help if you need it - as you have already. I would suggest checking out some basic fish keeping videos like these to get to grips with the area).

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