I have noticed that once I started filtering a lot of the live algae and the pressure would rise it would sound like I have air under the valve on the filter, and this wouldn't stop until I did a deep cleanse of the sand in the filter. Now that I am not filtering a lot of live algae I still get air under my valve and my pressure doesn't seem to rise. Today for instance, the filter ran for five hours and didn't raise one pound in pressure. Thought it might be the gauge so I picked up another one and it still seems to not be rising. When valve is in backwash, or circulate I do not hear the sound of air under the valve, I do hear it a little when it is on rinse. I do not have any air bubbles in the basket at the pump, just a few tiny ones but it has always been like that. I thought that it may not be able to pull in enough water so I slightly opened the floor drain as well as and still the same. Any ideas?
Also, just to be certain, the PSI should raise as the filter gets dirty correct? Is there any situation where I would not be able to trust the reading on the pressure gauge?