I know that keeping them as a pair isn’t ideal, which is why I plan on adding a third one soon. Kuhli loaches only require 20-30 gallons when in a school of 6 or more, meaning there is approximately 3 gallons needed per loach. Like I mentioned in my other comment, they are social creatures that will school with other fish and do not need to be in a species only tank. My loaches get along with my betta and they even play/nap together. This is far from impossible in a decently planted tank, as there is more than enough hiding space if they wish to be on their own. In fact my loaches are so happy that my female is gravid. Obviously if my betta was not so easy going, I would have not added the loaches as they would have been stressed and unhappy especially as a pair. But knowing my betta well and having done my research, I can confirm that it is possible as it is the case for my current 10g