I had 3 golden topminnows, 10 glowlight danios, 2 otocinclus and 5 peacock gudgeons in my 29 gallon. 5 glowlight danios and 1 gudgeon went missing. I blamed the topminnows. Moved them and put in a pearl gourami from a different tank. A few weeks passed. Nothing happened. Two days ago 1 more gudgeon disappeared. Yesterday another gudgeon disappeared. No bodies, no other fish acting any differently. Danios still chasing each other and gourami still hovering like a fishy drone. Two remaining gudgeons still doing gudgeon things. Otos still munching diatoms. Before yesterday's water change my numbers were as follows- 0,0,20 (nitrates in tap), 77 degrees and 8.0 pH. My filter is a large corner filter with no room for fish to get in. There's a gap in my lid but no fish bodies have been found. I moved everything in the tank and found nothing. I use a siphon but I keep it kinked while vacuuming so nothing gets past the tube if it enters after the first time the danios disappeared. That time it was possible someone got sucked up and removed by accident because I walked away for a minute with the siphon in so I've been really paranoid ever since. Is it possible my danios are harassing my gudgeons to death or my gourami is eating the ones that are left? I'm trying to stock this tank, not decimate it. And I bought five gudgeons to hopefully breed, so now I'm out of luck. Any ideas?