There are better ways to control algae growth than buying fish - what size tank, what filtration, what lighting, how long are the tank lights on for per day, any plants, any CO2 kit used, and how much natural light does the tank get?
i got mine from meadow view fish farm in droylsden, the fish in there are very healthy and quite cheap
Check out this link on SAE's - they get to 6" long, which is far too big for a 30L.
[URL="http/www.fishforums.net/index.php?showtopic=111583"]http/www.fishforums.net/index.php?showtopic=111583[/URL]
The Garra Pingi Pingi gets up to 5", which is also too big for a 30L tank.
[URL="http/www.aquaticcommunity.com/fish/pingilogsucker.php"]http/www.aquaticcommunity.com/fish/pingilogsucker.php[/URL]
I'd suggest you look at other ways of controlling growth. And btw, if the goldfish is a common goldfish (as opposed to a fancy goldfish) then the tanks too small for him too.
Unfortunately, you are wrong .He's only small atm...and anyway he's in a 15l now and he's fine so I think double the size will be plenty