Fish tank start up please

[SarfEasticated]

hi there, we have been given a 21ltr fish tank for my DD's b'day. Don't really know where to start. Want happy, fish, not fussed whether warm or cold water, but nicely coloured would be good. (DD wants pink fish!).
Thanks in advance!
SE

you'll need to 'cycle' the tank first before adding any fish

Does the tank have a filter?

21 litre is not huge when it comes to fishtanks the rule of thumb is '1 inch of (adult sized) fish per gallon of water' = which in your case would be 4.5

ye fishless cycling is a must, which usually tkes around 4-6 weeks but is really worth it for the welfare of your fish

when we were setting ours up i read that cold water fish were more prone to illness, and are messier. but i don't know how true that is.
we went for tropical though and they've been great, and much more choice colour-wise!

am sure EauRouge will be along shortly to give you some better advice than I can :)

The tank comes with a charcoal filter and a lid and a bag of gravel, we all prepared to wait to do this properly. If we want to go tropical what would be a good heater to get?

Four fish would be fine, would even be happy with more tiny fish.

I have a whole waterbutt full of rainwater, and I wondered whether to use that rather than hard London tap water?

it's not 4.5 fish - it's 4.5 inches of fish IYSWIM.

Basically 4 or 5 tiny fish.

There is a additive called tapsafe that you add to all water going in to neutralise chlorine/chemicals. - I no nothing about using rainwater

oops meant I no know nothing

21 litres is a small tank and there are very few fish that are suitable.

I would get a 25w heater (general rule of thumb is one watt per litre) and put one Siamese Fighting Fish in the tank. Tiny fish like danios or tetras generally have slim bodies which mean they like to swim fast - they are generally unsuited to tanks less that 2 feet wide.

Use tapwater but make sure that you dechorinate with something like Nutrafin Aqua Plus as this gets rid of chloramines as well as chlorine.

Now cycling means that you have to get the filter ready for the fish and they best way to do this is with a aquarium testing kit and some household ammonia. You see it takes a while for the bacteria which break down fish waste to breed and if you put a fish in before the tank is cycled then it will be swimming in it's own waste. This is potentially lethal to the fish. If you google fishless cycling then you will find lots of information about the how's and why's.

Ah thanks for the fish recommendation ? would a male be better than a female. Do they get lonely on their own? Any other breed recommendations? We only live in a tiny flat so no room for a larger tank anyway, so we'll have to make the best of it.

Thanks also for the info on cycling, I will get my research hat on this evening!

Males tend to be slightly bigger but male or female you can find some lovely, brightly coloured bettas. They are territorial fish and will fight any other fish of the same size. The won't mind being kept alone.

Some good tank mates would be some amano shrimp or cherry shrimp. However, if you get a particularly aggressive betta any additions will either be seen as a potential threat or a tasty snack.