How Many Fish In 64Litre Tank?

At the moment there is 2 small guppies, 2 neon tetras, 4 small Blackmoors, 2 small Barbs.
I need to get a few female guppies as they are chasing the other fish. Also some more tetras as they need some friends.
How many more can I have in there?

At a glance I can tell you the Black moor will need their own tank, these are coldwater fish and will get sickly in the warm water required by most tropicals.
 
Edit: Okay I hope you're sitting down.
Sorry to be the bearer of bad news, but...
Guppies need moderately to very hard water to do well long-term, while the vast majority of tetras need soft water, or they can develop kidney stones, among other ailments.
Barbs are fairly hardy, but are notorious fin-nippers when kept in small groups (5 minimum)
As to your question on stocking, even without considering the moors, which need at least 7 gallons each (your tank is 17 gallons BTW) then keeping your current fish in proper numbers would have you heavily overstocked.
 
I'd say the best thing to do would be to give us your water parameters (PH and hardness) and we can start from there.
PS,  your local water supplier usually has these on it's annual water quality report

that and do not get female guppies unless you want to be a breeder, as guppies, mollys Etc are huge breeders

I have to agree with Jeremy180: the tank isn't well stocked. Don't worry, we've all been there and done this kind of mistake, and it's not difficult to fix it.
 
Once you've told us what water parameters you have we can suggest a solution.

Zante said:

[I have to agree with Jeremy180: the tank isn't well stocked. Don't worry, we've all been there and done this kind of mistake, and it's not difficult to fix it.
 
Once you've told us what water parameters you have we can suggest a solution.

Click to expand...

OK, here's what I got...
 

I wish I had that water, my discus would love me!
 
The neons will be fine in that water, but in my opinion the tank is a bit short for them. You might want to consider rasboras as they are less "greyhound" fish than tetras.
 
It's be interesting to know what species of barb you have. If it's quiet peaceful barbs like rosy barbs then you could simply up their number to 8 instead of getting rasboras. If it's tiger barbs, I wouldn't keep them in a group smaller than 10, and they get way too big for that tank.
 
Guppies like hard water, so I'd rehome those two.
 
Regarding the black moors, they are a morph of goldfish, and as such will quickly outgrow that tank. Also as already mentioned they are temperate fish, not tropical, so they shouldn't be kept with any of the others.
 
If you prefer to keep the black moors I'd consider 150 liters as the bare minimum, but 250 would be probably better. They really do get big, and live a long time, much longer than cats or dogs.
 
 
If it was my tank I'd set it up as an asian swamp: lots of plants, a single betta, a group of small rasboras (like Trigonostigma espei for example). A few snails to keep the place clean of left-over food and debris.
Further down the line, once the tank is well mature and you have more experience add small group of kuhli loaches.

I would just like to add that while many tetras are too "hyper" for your tank, a few, like your neons, would be all right, it really all depends on the species.
Oh, Incidentally Do you know what type of Barb you have?