the care for butterfly loaches is the same as for a hillstream or boreno loach. they require highly oxygenated water and very high/fast waterflow. they are more or less a scavenger that will eat most any food found along the bottom, including blood worms and tubifex worms (which seem to be a favorite of mine) pellet, and wafer foods. you can also feed boiled squash or zuccini and leafy greens. while they do eat algae it should not be their main diet. personally i find these fish to require stable water conditions. Ammonia spikes, and wild temperature changes can lead to death. they are far more enterating and happy in groups, and their territory battles while intense cause no injury to the fish.
I used to have one of these. He stayed in the large area under the filter outlet most of the time, and ate just about everything. I lost him to a tank crash, though. Before that, he was perfectly healthy. One habit he had was he would attempt to sit on my cories when they went after the food he had targeted. That was fun to watch... He'd sort of flop at them, and they'd scoot away before they could get caught. I should mention that they're also called Hillstream Loaches, and may have 'Chinese' somewhere in the name.
They do "not" require highly oxygenated water nor very fast flowing water, just clean and moving water. This stated opinion has been proven many times over that it's irrelevant to the proper housing of this fish. Though their natural habitat is as described. Highly oxygenated and super fast flowing water, you don't need to have this to house them healthily. For example: the white cloud minnow lives in their natural conditions as hillstream loaches but has been captive bred in very slow moving water with co2 injected. HOB filters will do no good. They do like some flat rocks like slate or you'll only see their belly. 50 gal with a lot of co2 and they are doing fine. Thing is, you can make any fish adapt to co2 levels. Just not too high.