Goldfish And Gupiies/mollies...risk?

[Guppy_molly_love]

Most of my goldfish died, leaving two. My family wanted to buy some guppies and mollies because they breed a lot and we like it but my dad wanted koi fish, because he was afraid that the guppy fries would get eaten by the goldfish.
Please reply: 
Should we buy guppies, mollies,muppies(molly+guppy) or koi?

 

 

[fluttermoth]

How big is your tank and is is heated?
 
Do you know if your water is hard or soft?

 

[Guppy_molly_love]

volume: 24x30x38 cm
there is a water heater (automatically turns on in winter)
idk if it is hard or soft...

 

[Guppy_molly_love]

anyway, thanks to @fluttermoth for the advice and attention

 

[fluttermoth]

I'm afraid your tank is too small for anything but the guppies
 
Both goldfish and koi are really pond fish, that can grow to between a foot long (the goldfish) and two feet long (the koi). You should find someone with a pond to give them to, if you can, or they won't live very long
 
Mollies are smaller, but still quite large fish, getting to around 4 inches long.
 
Your dad might know about your water; if you get a lot of limescale in your kettle, shower head or washing machine, that means your water is hard.
 
Goldfish and mollies will both eat guppy and molly fry; even the parent guppies will sometimes eat their own fry. You need a bigger tank, with lots of live plants and none of the big fish, if you want to keep any fry to grow on.

 

[Blough]

I agree that your tank just isn't big enough for goldfish or koi. A common myth is that a fish will only grow to the size of its container, which isn't true. The truth is that a fish will die young in a container that is too small, rather then grow out of it. Before I knew what I was doing I had a tank with goldfish that was just a little larger than yours. The fish died within months, and I just assumed that it was how long they lived. Turns out, they can live for 20+ years when properly taken care of.
Also, in a tank that small you can't have a lot of guppies. If you want them to breed you'll have to have something to do with the surplus offspring, you can't just leave them in the tank. Another option is to buy just males or just females, some LFS sell them separately.
I have a question, what have you done as far as cycling?
 
I wish you good luck with your tank, and welcome to the forum.