Can you give me ideas please and numbers? Sorry for being a pain, but really don't know where to start with a little one. Had the big reef all planned out, but that won't happen.
The key to stocking with smaller tanks is knowing the habits of the fish that you want to keep, then, picking smallish fish with markedly different habits. For example...
green chromis
clownfish (depends on the species, most get too big)
bangaii cardinal
Technically, in theory, depending on the species, all would be fine in a 10g, if you just look at size alone, but the above is an unsuitable mix of fish for a 10g. Why? Because all three occupy roughly the same patch of water. They swim in the water column. Now...
Yellow watchman goby (YWG)
royal gramma
clownfish (depends on the species, most get too big)
This is another set of three fish. But if you look at the habits of all three fish, you have a very large contrast in habits and where they occupy the tank. The goby is a bottom dweller/burrower. The clownfish swims in open water and in the surface and then hosts something. The gramma is a mid-level cave dweller, weaving in about about the rockwork. See, very different habits. All three, similar aggression level too.
For smaller tanks, it's also preferable to obtain fish that really do prefer to be on their own. Like I have, in my 8g, a very large YWG paired with an equally large neon dottyback. A good combination. The goby is big enough to hold it's own and the dottyback is aggressive too. I doubt I'll add another fish to that system. Both are happy to be by themselves. My other 8g has a purple firefish and I'll be adding the black ocellaris that was in quarantine on Monday. Another good pairing. I may finish that tank off with a clown goby or a smaller, more peaceful goby/pistol pair.
Also, when stocking small tanks, avoid fish that have similar color patterns and/or shapes. For example, don't put a Royal gramma together with a bicolor dottyback. Yeah, we can tell them apart easy as pie, but a gramma is going to see another gramma in his eyes. And the dottyback, well, the dottyback will see another dottyback. Bad news for both.
For a 10g tank, I personally would stock it with 2-3 well-researched fish with markedly different coloration and habits and added over the course of some months and added in order of least aggressive to most aggressive. If you only find two, then that's it. The fish should exceed 2-4 inches in length, depending on body type. Goby & dottyback builds, which tend to be slender and long can be up to 4". The other types shouldn't be more than 2" or 3".
Does this help? There's a science to it really. You have to research the fish species carefully. And be warned many marine species jump, especially when kept in a smaller tank. A tight fitting lid is a good idea, always.
L
Was really hoping to get a pair of clowns. Is there anything I can keep in that size tank? If not I'll just sell it on again 
