Seeing as you only have 1 male, you may be able to get away with keeping all of them. Just watch carefuly and, if you see the females being aggressive towards each other (if the male is aggressive towards the females, reducing their number will not realy help - taking the male out altogether will), take a couple of females (the most aggressive) out and see if that helps. It's a tricky situation though you see - normaly, for this size tank, I'd say any more than 3 paradisefish is risky BUT, at the same time, with 4 females to the one male, you are spreading out any stress/aggression he is forcing on them. At the same time, each fish' space is limmited so the male is forced to hold a smaller territory and/or the females are more likely to run into his territory because of the smaller volume and get attacked. You also have the hierarchy between the females and they are more likely to clash between them in the smaller space - on the other hand, having 4 females means this hierarchical aggression is spread between them. In the end, it's down to the individual fish. Just watch them carefuly. Ultimately, you might have to take the male out if any problems arise.
Anyway, back to your orginal question, any of the smaller plecs - bristlenose, rubbernose etc, would work as a tankmate. Sticking to one is the best option.
Alternatively, a small group of otos would be an option but keep in mind the fact that they can be fragile and must have live algae and, later, green foods, always available to thrive.
If you'd rather go for a loach, there's plenty of options: 2-3 kuhlie loaches (most peaceful but you probably won't see them all that often), a couple of yo-yo loaches (lovely fish, quite peaceful, sometimes nippy but shouldn't pose a serious threat to paradisefish) or possibly some zebra loaches ( botia striata - slightly more aggressive but should still work), then there's the possibility of a group of gold zebra loaches (botia histrionica -small, peaceful, active, beautiful, may be difficult to find), 3-4 dwarf chained loaches (small and peaceful as well) and plenty of others. Most loaches of the 'botia' genus, provided they don't get too big, should make good tankmates. Also, research whichever species you are interested in thoroughly first as some can be quite nippy - the skunk loach, for example, is quite aggressive.
The 'butterfly loach' mentioned above, if it's what I think it is (hillstream loach), is not suitable as it is a coldwater fish, requires very well oxygenated water, a strong current and rounded 'river' stones for algae grazing. They are often mis-identified or sold under the name 'butterfly plec' as tropical fish - which they are not.
If you want to stick with catfish, the bumblebee catfish (psuedopimelodus raninus), may be an option. They get to about 4" and are good community fish. There's another 'bumblebee catfish' (leiocassis sp.) that is a little more aggressive and also gets larger.
Another option would be the upsidedown catfish and some other small syno species could also make good tankmates.
Just make sure you don't get anything that grows large enough to eat its tankmates!
If you don't want a catfish or a loach, you
could try a shark - I'm not guaranteeing it'll work with the more aggressive species but it's an option. The common 'more aggressive' species being the red tailed black shark and the rainbow shark. With these, make sure you only get one or they will kill each other. In fact, because this tank isn't very large, stick to just one shark (whether it's one of the more aggressive or more peaceful) or you will end up over-stocked.
The more peaceful species, that would probably do well with the paradisefish, are the siamese algae eater/siamese flying fox, the false siamese algae eater/false siamese flying fox/false flying fox, the flying fox and c. oblongus (which is found under any of the above names
). One of any of these would work but isn't a strictly bottom-dwelling fish. They are somewhat difficult to identify if you ahev nothing to compare between but, as they have similar requirements and all grow to about 5", this isn't much of a problem.
Regardless of what you go for, research it carefuly first. There are so many options and your paradisefish don't actualy narrow them down much
. I hope that was of some help anyway though - to give you some ideas, as a starting point. Remember to keep a close eye on your paradisefish and be careful not to over-stock with bottom-dwellers
.
