To recap, your skimmers and main drain work for normal pump and filter water flow. Your are now having problems getting adequate suction from a skimmer to vacuum. You were able to vacuum a few days ago.
Anything you vacuumed had to flow through the pump basket and impeller to get into the filter. Does your pump basket have any large gaps in it? I would check inside the pump around the impeller for debris that got caught there.
If the pump basket and impeller area is clear of debris then I would again look at backwashing or opening your filter and checking the sand. Have you ever deep cleaned the sand?
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Thanks. I'm going to check the impeller area tonight when I'm home from work to see if there is anything in there. I have not deep cleaned the sand myself. According to the prior homeowner, he had the sand changed last August. From what I read on here, that's around an every 5 year exercise?