I have a very similar situation in my 90g with my Botia kubotai
and Botia striata
, and very aggressive-feeding upper fish like Black Ruby Barb
, Congo Tetra
and Emperor Tetra
First, feed the flake foods at one end of the tank and immediately drop in the sinking foods at the other end. If this works, the loaches will quickly learn which spot their food appears.
Use a couple of pellet-type foods (rather than flake) such as the Hikari micro pellets, or the similar by New Life Spectrum. These will sink fairly quickly, and some will get to the substrate. My loaches like these, and even eat them as they fall.
Drop in a couple of sinking food tablets during total darkness once or twice weekly. Even though they are not nocturnal, the loaches will find this in the early pre-dawn, and dropping them in darkness means the upper fish will not see them.
Veggies sometimes work; a chunk of yam, squash, maybe cucumber, blanched. Will need to hold them down, there are tools for this sold by fish stores, or I have used a hollow clay plant pot that aquarium plants sometimes come in, about an inch long, with the food wedged in. The upper fish will likely eat this too, but the chunk can be large enough to ensure the loaches do feed.