Just purchased a Pentair 920 on marinas recommendation for an upgrade to replace our failed 5 year old dolphin nautilus, the nautilus would run one time and clean the entire pool, the 920 has now run 5 times and still has not cleaned areas of deep end corners and has about 4 spots it has not touched as of yet. Just fine dead algae easily comes up if cleaner goes over it, its just not hitting all areas... anyone else have this cleaner with same issue? Our pool is a 16x32 vinyl inground. 6' deep end.