Before vacuuming, is the water clear with sediment on the bottom? Is the "algae" sediment you're vacuuming grey or green? Are you certain the vacuum hose is properly pulling water? If it's slow, the action of vacuuming will certainly stir up the sediment.
If the obvious is fine, it sounds like either the cartridge has a tear in it or it's not seated properly in the filter canister. I moved away from the Intex cartridge filters a couple of years ago in favour of a sand filter. IMO the cartridges (even the cheap ones) catch a lot of fine material provided they're installed properly.
I'd try a replacement cartridge, and make sure it's centred and snugged over to the bottom lip by the pump impeller. Make sure the lid is centred and seated as well.