which one is more fun to watch - clown loach or oscar?

Clown loaches are lots of fun, but I stress loaches (plural). They must be kept in groups. They play together. One alone will be miserable, and no fun- it will probably hide and pine.

They grow BIG! But so do Oscars. I presume you have a great big tank. If not, get neither.
 
I have a 500 l tank (=ca 125 g) and 6,5 f long.
I was planning to take 6 loaches.
I was just concerned that maybe the loaches can be seen only at night but I'd like to watch someone during daytime, too. They grow slowly. I thought that when they were still small my tank would be not entertaining enough for many years...?
 
they eventually will outgrow it. i just had an oscar. he was very cool. hides a lot, but when he comes out he would put a show on.
 
go with the oscar. a 125g is not enough for the loaches. If you know that you are a responsible person, you could get 2 oscars for your tank. However, it would require extra filtration and also more water changes (3-4 every two weeks instead of once a week).
 
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