Don't hate it, it's just having a little tantrum.
It seems that alot of people are having more trouble than usual this year and Ben has speculated that some oversize pump / undersize filter combinations are pushing the dead algea through the filter grinding it into bits too small to filter. These filter / pump combos may have been fine for years but this year appears to be exceptional.
Adding a little DE is a good idea, it should help capture smaller particles. The gotcha is: adding a layer of DE on top of the sand bed in a small sand filter turns it into an extremely small DE filter.
With the DE in, your filter pressure should be rising.
Do you have the ability to take the multiport valve off the filter to inpect the sand bed?
Have you considered CarlD's suggesstion of adding a dose of polyquat 60%? It can act as a clarifier as well as an algecide - possibly making the cloudy more filterable.
Watermom's comment below is right on. If you use polyquat, don't add it until we've confirmed that you lose 1ppm or less overnight and have 0.5ppm CC. Then keep a close eye on your FC and be sure to keep it above 3ppm as the polyquat will drop your FC.
You'll get there. We'll help.
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