Numbers In A 20 Gallon

[Cosette]

if i get guppies, peppered corys and dwarf gouramis in a 20 gallon tank, what would be the recommended numbers for each?

 

[attibones]

6 corydoras
6-8 guppies
1 dwarf gourami

I think this would suffice. However, you don't have any middle swimmers. Guppies and gourami are both top level, which may create a few problems. You could substitute the guppies for perhaps cardinal tetras or something like that, which would give you activity on all three levels of the tank.

 

[N0body Of The Goat]

Tank volume only tells part of the story and gallons can confuse people (imperial gallons are bigger than US gallons), one reason why I use litres.
 
What are the tank dimensions in centimetres, please?
 
Some general concerns about the fish combination you mention...
Guppies are great for smaller tanks when it is an all male group, a mixed sex group will result in a massive population increase every month or so once the initial group matures.
 
Peppered Corydoras are not "mainstream tropical" fish and as such, they should not be kept at mainstream tropical (~75F, 24C) temps all year round, doing so will knock chunks off their lifespan. They are "temperate," typically do great in a heaterless tank that spends about half the year between 16C and 20C, with a summer season where the temp approaches ~24C for a month or so. There are lots of temperate fish in the hobby, a tank can be stocked with lovely fish and not cost a fortune on heating electric, second only to lighting costs (often for the benefit of demanding plants).

 

[Noahsfish]

Yeah, depending on where you live either cardinal or neons might be a better fit, but sometimes either the cardinals or neons can be quite sensitive, again depending on where you live.