Small Hexagonal Tank. Max Number/type Of Fish?

[ole tarantula]

Hello, this is the first time on the fish forum. I am a complete beginner trying to find out as much as I can about a very broad subject.

I have a 20Litre tank from Pets at home which I ran for a week before adding 6 neons. A week later I added 2 Mollies. I am thinking of adding a couple of Platies too but don't know whether this will make it too crowded and difficult to manage in terms of water quality.

The tank I have came with a carbon filter, a mechanical filter (sponge) and three plastic balls which suposedly form a biological filter. Can anyone offer any hints and tips as to getting the best out of this arrangement. Presently I am doing 15-20% water changes every 2 weeks. I dont have a nitrate test kit but I have been checking the pH which remains stable at about 7.5.

How good an indicator is pH in terms of water quality?

 

[@ombomb]

I have a 20Litre tank from Pets at home

that's basically a vase I'm afraid

which I ran for a week before adding 6 neons.

uh oh...

A week later I added 2 Mollies.

I am thinking of adding a couple of Platies

STOP!!!

You have made a fairly common mistake of jumping in with both feet without doing any research I'm afraid.

You've bought a tank that could house a handful of specialist species, most likely a Betta (Siamese Fighting Fish) and very little else. The Neons have little or no chance of surviving in there in the short term and the Mollies will suffer in the medium term.

My suggestion would be to return the fish you have immediately, decide what you would like to keep and then buy the appropriate equipment having researched their needs.

***EDIT***

How good an indicator is pH in terms of water quality?

Basically useless, but a sudden drop in the pH could indicate a sharp ammonia spike.

 

[Marshall..]

Get a larger tank it is much easier to look after fish in higher volumes of water.You could add an external filter of reasonable size to help with more volume but you are already crammed with fish for that size tank and I don't think it will be good in the long run sorry.

 

[ole tarantula]

Get a larger tank it is much easier to look after fish in higher volumes of water.You could add an external filter of reasonable size to help with more volume but you are already crammed with fish for that size tank and I don't think it will be good in the long run sorry.

Thanks for your comments

What would be the minimum tank size that could support the fish I already have?