I'll get some Otos this weekend as well as maybe some Corydoras pygmaeus as I do love my corys!
I would wait on the otos until the tank is well established with some common algae [maybe it already is?]. Otos are to the point of starvation when we acquire them and without a good amount of natural algae they often die soon.
Corydoras pygmaeus do better in smaller tanks. Mixed in with the larger cories never seems to quite work, at least not in my experience. Not that the larger pick on them, no
Corydoras species does this, but the pygmies seem to get lost and not do so well. My group in a 10g spawn regularly and have for several years now. They need sand and cooler temperatures, though this applies to all cories anyway, but with the pygmy it is mandatory.
They're definitely Corydoras adolfoi, though yesterday I picked up 3 more and 1 seems to have black in his dorsal fin, leading me to believe he is a duplicareus. This morning I woke to see all 6 of them sat in a line, so at least they seem to stick together.
Photos would help with ID, sort of. Externally, the black dorso-lateral stripe on
C. adolfoi is usually much narrower than on
C. duplicareus though sometimes this is not that easy to see, but generally both this band and the eye band are much broader. On some of my fish the lateral band extends more than half-way down the sides of the fish. The black may extend up into the dorsal, to varying degrees depending upoin individual fish--on some of mine the entire fin is coal black.
The orange post-orbital fleck on
C. dupiocareus is a much brighter orange when compared to
C. adolfoi, (though this too is not always so obvious depending upon the condition of the fish) and it remains brightly coloured as the fish matures which is apparently not the case with
C. adolfoi, usually. The only absolute ID is the pectoral fin spine ray, which is smooth on
C. adolfoi and slightly serrated on
C. duplicareus but this requires viewing under a microscope to see clearly. Having said that, it is very rare to see true
C. adolfoi these days, as they are just not as brilliant in their pattern and colour by comparison; the "adolfoi" name is almost always given to
C. duplicareus by exporters/importers at least in NA.
There are other closely related species too;
C. imitator (identical in pattern/colour to
C. adolfoi) and
C. serratus (identical to
C. duplicareus) but both of these have the long snout as opposed to the blunt snout so that is pretty obvious. Some 12 new species were discovered during the 1980's and 1990's, each endemic to specific southerly-flowing tributaries of the upper Rio Negro, and having very similar cryptic (camouflaging) colour patterns. When viewed from above in the habitats, the colour pattern of all these fish cause them to blend in with the twigs and branches that litter the buff-coloured sandy streambeds. The patterns include a buff-coloured body with a black dorsolateral band (that may only be partial on some species), a black eye band, and an orange post orbital fleck in the shape of a "V" when viewed from above, the intensity of which varies between the species.