Active, friendly, and hardy fish are pond loaches that are often used in an aquarium as starter fish. They could become "sweet" to humans, enabling body interaction and feeding by hand. They are extraordinarily peaceful. With goldfish, they get along better.
Given more room and greater numbers, the loaches would be more aggressive. Single pond loaches prefer to spend hiding most of the time. They're going to spend a lot of time hiding or standing still, but a place to stay should be provided that's going to have shade and shelter. They can swim through tank decorations, and driftwood both work well for that. The average cover should be enhanced with tape or other barriers due to its jumping capacity. But if you eventually find your loach one morning black and dry on the concrete, try to put it back in the aquarium.
It will normally recover and slither away and create a full recovery. It has been documented in certain cases that they can survive off a tank for up to 3 days. They can even fly up tubes and live in filters, so search there if one day your pond loach doesn't turn up for a headcount. Pond loaches love exploring in the soil of their tank and trying to crawl themselves, so ensure your soil is fine suitable for them to dig in. If you hold live plants in your aquarium, the loaches will uproot them, so weighting your plants is a good idea.
The pond loach is also unusual in that during periods of stress; it can often bury itself in the substrate. This also concerns new owners, as the fish will "disappear" only to "reappear" later shortly after being added to the tank.
These loaches may help mitigate snail infestations in freshwater fish tanks due to their appetite for snails, although many have claimed that although pond loaches eat snails, they do not eat them at a high enough pace to cope with an infestation.
The fish enjoy a pH of 6.5-8.0, but even for prolonged periods of time with a little negative reaction, they can tolerate much more acidic conditions.