First Time Pool Owner - Two questions

We have recently installed a 45k gallon, in-ground pool in the fall of last year. The pool was operated for approximately 1 month and then was professionally winterized. This spring the same company started the pool up for the summer.

Included with our purchase was the following: a 540 sqft Pentair Clean and Clear cartridge filter, Delta UV system, IPS Chlorine and ph control system, Intelliflo circulation pump, and Hayward heat pumps.

The pool is use approximately 3 weekends out of 4 and remains covered by an automatic cover the remaining time. Meaning that the pool is only used about 6 days a month and the cover is darn near air tight A professional pool service performs cleaning, equipment maintenance, and chemical monitoring weekly.

We are very happy with the pool with two exceptions;

1) Some grey staining which appears as modeling in some areas, solid grey staining in others, and evenly spaced (8") horizontal grey lines in others. The issue is getting more noticeable.

2) The other issue is the frequency of cleaning the filters require. I have cleaned them twice this summer and pool maintenance service has cleaned them once. I was told that you can tell if the filters are clogged if the water pressure is above a certain level, but I notice the heaters shut down for lack of flow long before the magic 35 psi is achieved. So each time the heat pumps will not work, I have cleaned the filers and each time there is very little "dirt", rather there is a grey sludge that rinses off with direct hose spray.

After poking around the interweb I have read a lot about improper plaster installation and "dusting".

I would love to hear some thoughts and suggestions on how my pool is behaving and if you see some things I should be looking for.

Thanks.