How do I ID the *real* algae eaters ?

Hello,

A while back I remember several discussions on the subject of algae
eaters. There seem to be a few fish that look similar, some of which eat
algae and some of which eat other fish ;-)

I would like to buy an efficient algae eater (or two, depending on *how*
efficient they are !!), but I currently have a very peaceful community
and don't want to upset the balance.

What fish would you suggest ? Anyone know the way to ID them accurately
?

Current fish :-
2 large golden gouramis
4 large tiger barbs
8 glowlight tetras
9 harlequin rasboras
3 synodontis velifer, one about 5", one about 4" and one about 3"

Tank is reasonably well planted, 150 litres, soft slightly acidic water,
120W lighting, DIY CO2 injection. Three large pieces of mopani wood, one
very large amazon sword, two small ones, assorted other small plants.

Any suggestions/info welcome. TIA

--
Alan Silver