I fully concur with 1077's advice.
Nitrosomonas and nitrospira bacteria can begin to die off in less than a day if ammonia is not present. These bacteria only live as long as they have "food" (ammonia and nitrite respectively), and if this increases beyond their present numbers, it takes approx 9 hours for nitrosomonas and approx 20 hours for nitrospira to multiply which they do by binary division continually in those time frames until they reach a number sufficient for the "food."
If your fish are in an existing tank, I would move one over, wait a couple days and test, then move another, etc., moving the three gourami at the same time.
By the way, using "old" water is no benefit. The bacteria colonize hard surfaces under water, so filter media, plants, wood and rocks, substrate will carry over bacteria, water will not. However, in your case you may have transferred ammonia with the water, and that will feed some of the bacteria for bit longer. Also, at an acidic pH your ammonia will change to ammonium which is basically harmless to the fish, so it will be the nitrite stage of the nitrification cycle that is critical in your case.