Fish huddling down in corner of the tank

Question
I've had my 55gal tank set up for 3 months now. I have 2 balas, 4 danios and about 15 guppies. My filter is a Tetra whisper, but I'm not sure which model. It is a large, internal filter that came with my 55 gallon tank. The PH runs 6.8 - 7.0, Ammonia is at "0", nitrites are at "0" and so are the nitrates. I change the wanter every 3-4 weeks, about 30 gallons at a time. All of my fish are pretty much middle swimmers, but also wandering all around. The last few days all of the fish have been huddling all together in the bottom front corner of the tank. Just "treading" water. Even the guppies. I thought maybe the water was too warm at 78 - 80 degrees Fahrenheit, so I turned the heater down just a click or two. The water temp has only dropped to a solid 78 degrees. The water is clear. There is plenty of space for the fish to swim from one end of the tank to the other.  My tank is wider than tall. The balas also often  run up and down the glass with their nose against it. They eat well, they look fine. I'm not sure what is wrong and I don't want to lose them. Any suggestions?

Answer
Hi Janet;

Look very closely at the fish for signs of parasites or other disease. The irritation that parasites cause can make fish feel strange and just want to hide in weird spots. Any spots, dots, fuzzy patches, blotches, etc., could be signs of infectious illness or parasites. Look at them from different angles and with a flashlight too. One protozoan parasite simply leaves a very fine golden dust on the fish. It's called velvet. Let me know what you find, if anything.

If there seems to be nothing on the fish, have the water tested again from a different kit. It's possible the tests were wrong. It happens sometimes.

At Your Service;
Chris Robbins