I've been out of the hobby too long and have forgotten too much.. right now, all I have is 3 tanks of guppies and in all three I have fish rubbing themselves against the plants ("glancing"). No visible parasites, no fungus, not even clamped fins. What could be the problem, and what is a treatment that would be safe for my plants? Parameters: the pH is about 6.8, TDS 148 with the water having a lot of calcium carbonate, no nitrite, less that 20 ppm nitrate. Water is crystal clear.