About a week or so ago, my husband was doing a 25% water change, and we noticed that we had build-up of some sort in all of our tubing, and its in our spray bars as well. It does clog it up a bit, but have been clearing the holes when it happens. When the gunk comes out of the holes, it looks whitish. Is this normal, or do we need to be treating this as a problem? Thanks in advance! We clean the filter every few weeks, unless we see a big problem. We've had the tank(60 gal) about 2 months now. We have 14 fish(plus several fry).