My brother has a 10 gallon tank with a betta fish and 2 cories. Water test showed no ammonia or nitrites. The betta fish is sometimes near the surface on his side and sometimes resting on the bottom breathing heavy. The cories were added last Monday. They get along pretty well. They pretty much ignore one another. He hasn't been fed since yesterday afternoon, so probably not sbd. No signs of dropsy. Does anyone have suggestions of what could be wrong?