kapo
New member
When you have sand in the tank, you're supposed to give it a stir up every so , every couple of days or weekly, either with your turkey baster or siphon/gravel cleaner as pockets of anaerobic gas can build up within the sand layer as well as bits of food or waste getting trapped beneath it, particularly where there are plants or decos/hides; so this may very well have caused the problem.