The problem with suggestions is that what someone thinks is a perfect group of catfish, another person will think that it's not particularly good idea.
The obvious choices are:
1. Large group of corys - you'll have lots of enjoyment of them wizzing around looking for food - in 100gal tank, you can keep a fairly large number of them - depending on size, 30-50 would probably work. Examples:
,
,
- there are hundreds of others...
2. Medium size group of smaller plecos. Again, with a large group, 10-20 of them (of one or two species) there will probably be some fish on show at any given time. Some examples:
,
,
- agaain, many hundreds of others.
3. Small group of medium plecos. As above, but smaller group. Examples
,
- several dozen others...
4. Community synodontis tank: small or medium sized Synos - 6 to 20 depending on which you go for,
,
,
,
, and many others.
5. Small Pimelodus tank: a group of around 10
?
6. Woodcats setup: small or medium sized Woodcats, such as
,
,
- and a whole number of others. These will probably hide most of the time...
These are but a few examples of what you could do... After all, there are 2700 species in the database, and I'd expect about 1000 of those would work in a 100 gal tank...
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Mats