For now... Your pump filter looks dirty. Is that just a bad picture?
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A pic to the right, please?
The round convex glass/plastic piece about 6-8" in diameter right past the pump in front of your filter
Yup, that's it. it's called your pump filter and basket. Still looks like crud in there. Glad you are cleaning that out periodically. Can you get a picture to the right? Looking for shut-off valves of some sort.
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It still looks dirty in there. There is a basket inside like a colander. Are the "holes" clear so that water can flow through it?
Have you checked for air in your filter? I have the same model just different size filters. You turn the gauge base CCW towards OPEN position. If there is any trapped air, it gets released out of the small hole in the side of the base. Then water squirts out, so be ready to twist it back around. I have a small leak in my inlet o-ring and if I don't release the air once in a while, I will start to show lower PSI and bubbles from the returns.
On to your staines and a question for everyone following.. If it is calcium staining, is there a way to find out for sure?
Will testing the water for metals help ID the stain?