I have 3 tanks in my house. In each tank I have 2 Siamese algae eaters (SAE's). They are always cleaning the leaves and rocks. I have never had any trouble with them and they don't stake out territories or chase other fishes. I prefer them to the Otocinclus, as they are much hardier. Also, unlike Otocinclus, they can take other foods other than algae. Unfortunately, there are a few 'fake' SAE's for sale. The true one will have 1 black stripe starting from the nose to the fork of the tail. Their fins should be transparent and the body should only be 1 colour. If you choose the correct one, you will be pleased with the result of a very clean and clear tank.
In our two tanks we have one flying fox, one chinese algae eater and a SAE algae eater (we had two but one suicided). The flying fox rarely eats algae, but keeps to itself pretty much. The Chinese algae eater does a bit of algae eating and a bit of chasing other fish, although it can't seem to swim for very long and tends to give up pretty easily. The SAE, on the other hand, is probably the most chasing of the fish. It doesn't do any harm, just chases other similar fish like bala sharks and flagtails. When it catches them it seems to not know what to do and just stops next to them, but it chases fish more than any other species we've had since the red-tailed shark. Very active and constantly eating algae though - I still love the guy!
The SAE is often said to be too active for sensitive fish like Discus. I have kept 5 in a 250 L aquarium with Discus for close to 4 years. In this time I have never seen them stress the discus which, I feel they are relaxed by the presence of smaller schooling fish (even if they are active). In addition I have never seen any evidence of the SAE's eating the Discus' mucus coats. They tolerate higher temperatures up to around 30°C, but I have found that this reduces their lifespan to around 3-4 years.
I bought two of these guys for my 200 L tank about half a year ago, and they went straight to work on my beard algae. They chased each other, my giant danio, my angelfish as well as my chinese algae eater. I then came home one day to find that one of them had apparently scraped himself on my driftwood or something, and soon died. The one left then started nibbling at one of my angelfish's fins, argh! I then moved all of my fish into a smaller tank (150 L), while I redid my other one. He continued his harrassment on the angelfish, but then he started going after my rasboras as well! Poor little guys! When I finished my 200 L tank, I moved him and my giant danio in it, thinking, 'Ha! He can't bully him!' Turns out that I was wrong. Apparently once you have a taste for tail fins, you must have more. I then bought four more giant danios, and the fin nipping as seemed to cease, (though he likes to chase the little ones once in a while). This new behaviour may have been because there was an algae spike (lol). I will get him one or two more friends in the near future to combat my algae, and to keep him occupied. I'd also like to include that he demolished my Hygrophila polysperma in my 150 L tank, but it is now recovering nicely. Now his diet is Rotala wallichii, as well as any algae. Well, at least that plant was cheap...ah well. Overall, a useful fish, given the right tank inhabitants...
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