Bought my new cartriage filter today

[waste]

Just a thought on keeping the algae out of the cartridge.
I don't know your pump & filter set up, but is it possible to disconnect the piping from the pump to the filter and temporarily hook up a waste line to the effluent side of the pump? This could be a big headache, so I offer this- is there enough room to install a 3 way valve between pump and filter the 3rd port could be used to bypass the filter just like the 'waste' (no relation ) position on your old multiport. *
Should either of those not be feasible, you could remove the cartridge, put the filter back together, isolate 1 return (by valves if applicable or with the winterizing plugs put into any other returns) and screw in a 'Backwash fitting' (SP-1091-Z-7) attach backwash hose (vac hoses work best, but you'll be using yours to vacuum) run the end of the hose wherever you want the slime to go and start vacuuming

* If you do this DO NOT USE a Hayward SP 733 valve, they are notorious for leaking and I believe that they are being discontinued so the replacement parts you'll need almost yearly will be unavailable (use something like the ones Jandy makes). Also, put a 1 1/2" female adaptor right out of the valve, you can screw the backwash adaptor into it (or a treaded plug, if the valve ever fails)

Dave, I see that algae all the time, water is crystal clear but the bottom is covered with a nice layer of green it cleans up quickly with a leathal dose of bleach, though a good brushing just after adding the cl eases the process.