Fish sitting at bottom of tank - seems ok otherwise?

6 year old oranda, in a 110 litre tank, with a 7 year old comet. The comet is in fine fettle but the oranda has been spending a lot of time sitting at the bottom of the tank, although he swims about now and then, and comes up for food. He's not swimming oddly or anything. He did have a few white specks on his head, but they are not as obvious and think they might be going away. I had another comet which developed finrot and swimbladder problems, and died a a few weeks ago, in spite of water changes and treatments. I do regular water changes (a third every 2 weeks) and hoover the gravel, etc. I gave them some peas in case he is constipated, but is there anything else I should be doing?