180 ltrs is too small for clown loaches in the long run. They are shoaling fish and grow big.
Angels need a high tank, not sure of the proportions of yours.
Corys are an excellent suggestion. Need to be in a group of 4 and 5, and the substrate needs to be kept quite clean, but otherwise they are easy to cater for. Avoid panda corys though at first as they are more sensitive. Bronze or peppereds are a good choice. Gender ratio does not matter; they are not macho fighters but more into giggly cuddly sex (well, that's what it looks like anyway
).
Livebearers are another good suggestion. There is an excellent introduction thread in the livebearers forum; in particular, take note of what it says about gender ratios. 2 swordtails or 2 platies are not a good idea unless they are both females. A male will harrass a lonely female to exhaustion, 2 males may well fight.
Gouramis again are often best as a female only group or 1 male with a small harem. On no account try to stick 2 male dwarf gouramis in a tank together; they will rip each other apart.
Some tetras such as neons and cardinals are sensitive to water stats, so better in a mature tank. (and they don't really like hard water either). Black widow tetras are said to be hardier.
Be careful not to overstock.
Good luck!
