I think it's time for new filter sand? My PSI climbs from 15 to 20-25 in a matter of days, and my water is quite clean. I just did the deep clean last night and noticed my sand has been warn down into tiny smooth spheres! I don't know how old it is but I brought a sample into work to take a look at under the scope and share with you guys here.
On a side note, what does the air relief tube do? I pulled it out to get the diffuser off last night abut just kinda stuck it back in when I was done. Where is the end of the tube supposed to go?