What’s this residue on my filter cartridges?!

[MostlyCanuck]

Hi folks - went to clean my cartridges today after closing the pool a few days ago and I noticed they are completely covered with what looks like white/gray/blueish granules - see pics.

What is this stuff?!?

It did not go away by hosing it down. Now the cartridges are soaking in TSP - hope that will help..

I don’t add any pool store potions to the pool. The only granular stuff that’s gone in would have been stabilizer (cya) - that I dissolve in a sock in front of jets and in the skimmer basket (also in sock). So my guess is that’s it - somehow it didn’t fully dissolve (over months?!?) and deposited on the filters?

For completeness, I think maybe once this year I had to add some borax if I recall correctly but that’s it. Other than that it’s just muriatic acid and the occasional liquid chlorine boost…

Any other suggestions?

 

[Rancho Cost-a-Lotta]

Are you able to scrape enough off to put a drop of muriatic acid on the substance? If it fizzes, it is calcium based scale. Are you seeing anything similar in your Dolphin's filter basket?

 

[MostlyCanuck]

I did scrape it off - no fizzling or sizzling when added to muriatico acid. It did turn oddly yellow though- see pic above..

I also noticed a large amount of what may be similar matter (maybe - my guess) is also deposited on the sacrificial anode , which I believe is made of zinc:


When I soaked the filter cartridges in MA, there was some bubbling action but not that much and it seems these haven’t fully gone away.

Any chemistry brains out there hazarding a guess as to what this may be?