fish behaving strangely

Question
Hi Jaymie, first off, my dad and some of my friends call me Jamie, its a good name! Now on to my question. I have a 20 gallon tank thats currently holding 3 gourami (opaline/gold/blue) and 2 killifish. Over the past 3 weeks the gouramis out of no where go bezerk bulldozing through the decor, even undoing the filter plug in the tank. Doing this somehow puts the killifish into the trance....and then all the fish just carry on like in never happened. I've noticed though that the gouramis are hiding ALOT more then they've ever doe before, and almost resting on the bottom. The killifish seem fine, not acting unusual. I've had this tank aperating since April 1st of this year (2012)an over a month ago a fungus(i think it was) attacked my tank somehow, I figure from a fish i purchased that died shortly after. This disease wiped out my 5 corys who i really enjoyed. It was an instant overnight attack. They had white flagelle on their bodies. The last 2 remaining I put in a 2 gallon tub with fungus cure, and it disappeared. Within hours of returning to the tank it was back. I was wondering if you have a idea what exatctly that was? I thought it was fin rot, but didnt affect the gouramis or the killifish, just the corys and 2 cherry barbs that I had, and would have an effect on the remaining fish and their odd behavior? I used to do a water change every 5 days when I had more fish, now its between 7-9. The water temperature is around 73.

THank you for your time,    -James

Answer
James,
They could be reacting to water issues. Have you tested your water for nitrites and ammonia? Both of these have to be zero at all times. Make sure you test your water weekly and you do the water changes weekly. If after you test the water, and the readings are zero, let me know.