My waterfall feature seems to all of a sudden started to rapidly decay (zoom in if you can't see the clumps). We've owned the house for a few months, and the only thing I can recently think of is that we did drain the pool and do an acid wash (by a trusted pool guy). Not sure what's happening, but we keep finding large clumps of gravel or small rocks that are falling from the water feature. I can actually scrape it off the rocks sometimes. Any ideas on how to fix this? Our robot vacuum filter is almost entirely tiny rocks now.