I have a 25 gallon tank with 10 cardinal tetras and one honey gourami. We've had the tetras for a year, and they used to swim around the tank. Six month ago we moved them from my office to my husband's office, which is often kept darker than mine. Not long after that move, they started hiding in the corner. I have tried some slightly different configurations in the tank, water conditions seem good, we've done plenty of water changes, lowered the light level in the tank.... But they stay in the corner. Occasionally one will start to venture out from the corner, but when the others don't follow, he returns to the corner.
At the last water change, we took them out of the tank and temporarily put them in a 3.5 gallon tank in my office while we did a really thorough clean. We replaced with new (and more) fake plants in the hope that more cover would be helpful.
They seemed far happier in the little tank. They swam around a lot, didn't seem particularly skittish when I'd walk past the tank, and never hid in the corner. After the deep clean of the larger tank, we moved them back and of course, they are back in the corner.
Should they live in a smaller tank? Or is there something I should be doing do to help them feel more secure. The gourami leaves them alone completely, so shouldn't be creating stress for them.
Ideas?
