Ok, that explains part of the problem. The cartridge is a bit small for the pool.
It's OK as long as the water stays clean; but if it gets bad, it will quickly get overwhelmed.
You need a full SLAM and you will have to cycle the cartridges as needed.
DE is not good for cartridges, so don't add any more.
In the future, if the pump goes down, maintain the chlorine with liquid chlorine and brush to mix.
Even with no pump for two weeks, you can keep the water from going green, even in the summer.