I'm not sure on the tank size for Siamese Algae Eaters (SAE), I've had a pair in a 180L for 3 years already. The problem is, the SAE gets lazy looking for food very quickly, so needs to be really hungry (3 days + with no food) to revert back to cleaning your tank. Obviously you can't starve all your fish for 3 day stretches, so IMO SAE are good for very short periods of time when you are not feeding.....better to find out why you have algae and prevent it from the source. Again, no expert, but if you are like me, you might have your lights on too much. In the beginning I wanted to see my fish all day (I work from home), but that's too much light for algae, better to get it down to 6-7 hours, with an hour break in the middle. some websites suggest fish don't really care if it's night or day, though I know my nocturnal fish know when its lights out time and come looking for their nibbles!
SAE's grow big, are territorial if fewer than three, and prone to certain diseases (google FFHLE), they also have small swim bladders and prefer to rest on low lying leaves or bark where they can rest. Seeing as you are in the UK, the hardest part will be getting true SAE's.....so many other fish look like them! I scan my closest 15 stores on a 3 month basis and have got only 1 SAE since december
Even then the store didn't know them had him until I pointed him out
Other forum members will chime in here and advice on lighting....I only express my own opinions!
