Going to try to list what i know and hope someone has a good idea whats wrong.
Background
1500 gallon pond
2 bottom drains going to ultima 2000
1 large savio skimmer going to same filter.
Slightly Overstocked pond but water quality always good for 2 years now except string algree going on 1 year
Recent noticable changes are a huge growth in tiny black snails, and a spawn 2 weeks ago. Water quality was back in check within 1 week and all seemed well.
No noticable water pressure differance when pond is running
Problem
When to backwash the ultima 2000 and it just didn't sound the same, as soon as i flipped the power off you can hear water rushing into the filter and then when i turn value to backflush i can barely hear the media inside turning ( and the water ussally twirls in the sight glass but now just looks almost still during back flush) and the water coming out was like regular pond water and not the nasty water i always get without fail every week. The backflush pressure of discharge water is also much slower then normal. Any ideas what is the issue?