Advice need on stocking an aquarium

[gwp90]

My sister recently moved home and the previous owner left her a 4" common goldfish (I think) and told her to flush it. My sister wouldn't do it, but she also didn't want the responsibility of looking after the goldfish, so it wasn't being looked after, whilst she tried to find it a new home, so I ended up adopting it, to give it a good quality of life. I bought a 19L (4 gallon) fish tank to house it in. I then wanted a snail to help with algae, but none were in stock, so I got a 4" gold weather loach, with advice from a pet shop. After this I began researching online and have came to the understanding, that this tank is far too small for even a goldfish, never mind a weather loach too. Since getting the fish, I've developed a bit of an aquarium bug and I'm getting immense pleasure from keeping fish. My first goal was always to give the goldfish a good home, but now I'm doubting I can do this with only a 19L tank, so I've been looking into a 250L (50 gallon) tank. I only have the space to fit a 110cm wide tank, and the biggest volume tank I've seen with a width that fits into this space is 250L.
My question is... could a 250L tank house 2 common goldfish and 4 weather loach? (assuming the 6 fish are all fully grown) or would it be overcrowded? or would there possibly be space to house another 1 or 2 species of other cold water fish? I will be getting a filter with a 400L rating and will have real plants in the tank.
Another question is... The 19L tank will be turned into a hot water tank and I will be getting a Betta to house in it, but would it be able to house 2 Bettas?
My main goal is to have happy and healthy fish. I would love to have at least 2 of each species, so my fish have another of its own species to interact with. I read that weather loach are best to have in groups of 4+, hence wanting 4 of those. I don't however want them to bred, so are there any tips to prevent this or will I just have to hope they don't and be prepared incase they do?
I've been conditioning my water, added bacteria to cycle the tank, have been feeding a variety of foods (flakes, bloodworm, vegetables and algae wafers) and have been doing regular 50% water changes (50% due to the small size of the tank).
Gareth
P.S. any advice on caring for fish will be highly appreciated.

[loachy dance]

Friendly loach guy here!
I usually recommend a minimum of 90 for that much fish. Having said that, it can be done, but water changes will need to be much more frequent, especially as goldfish are basically slobs.
I think 3 loaches you could getaway with. I personally dont hink you need a second goldfish, but others may disagree. They are simply not as social as loaches, especially if youre comcerned about space.
This could be a fun tank, both species can be trained to eat from your hands pretty easily once hey are used to their environments. ( and potentially cheaper as neither needs aheater).

[Fresh2o]

Only put one beta in that tank (4g) because of temperament and size of tank.


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[gwp90]

Hi, thanks, I think I was just assuming all fish were as sociable as each other. How much tank would you recommend for 3 weather loach and 1 goldfish? (assuming they're fully grown).
...and how much tank for a fully grown betta?
I suppose with 1 goldfish and one betta, it's only the loach I need to worry about breeding, but I've read that's a rare event?

Gareth

[loachy dance]

Its super rare, but could happen. Its easy to sell healthy young loaches though.

Back to the other part, loaches are much more social, like dogs. They will form a social hierarchy with a dominant loach leader. Many cichlids do this and tetras and barbs. Goldfish donot. Betas donot usuqlly stay in groups, setting up individual territories, some other cichlids follow this model.