Been in this hobby for over 45 years and I've seen just about everything. But, this new to me. Before anyone asks, water tests are fine. I added tablet fertilizer in my planted tanks Tuesday morning. Early this morning (Wednesday) while feeding my fish their breakfast, I noticed a bubbly foam on top of the water. I am under the assumption that the fertilizer has something to do with the sudden appearance of the foam. Fish are doing fine, and not all of the tanks fertilized are "foaming". I have not check for phosphates as of yet. Too much fertilizer? Water too soft? A combination of both? Water in the three tanks is testing 6.8-7.0pH. Doesn't seem to be a real problem, yet, but could it be?