I have had a school of 6 corydora swarzi for about a month now and they seemed to be pretty active from day to day bases. A couple of days ago I noticed the school went from 6 to 5. I looked around the tank and was unable to spot the last one, since the tank is heavily planted. I didn't think much of it, but I have only seen 5 corry's for a couple of days. Any advice?