I'm 6 weeks into pool ownership and it's been a rough ride. On a tip from a friend this has become my new go to site, so hopefully things are going to get better from here. At any rate, I've just finished killing off my third algae bloom of the young season. It took extremely high levels because I didn't understand the CYA effects of tabs for the first few weeks. This latest round may have been mustard algae, but I can't be definitive on that. After getting the pool to the 'milky' stage my sand filter cleared the first bloom in about 24 hours, with the corresponding pressure rises/back washes that I expected. Unfortunately for blooms 2 & 3 the story has been different- despite a healthy outflow from the return, the sand filter shows neither an increase in pressure, nor an indication that it's filtering anything out. My local pool store is happy enough to roll out a 'side system' DE filter, which clears the water, but functions more as a sales pitch than a helpful diagnosis of my current sand filter. Any ideas on why my filter has gone from perfect operation to 'stuck at 18 psi' would be greatly appreciated.