Your cartridge filters are in ground? Like buried? It's also weird to me that you have two. Seems to me that if one was dirty then the other would be irrelevant. Unless you can switch between the two. If so that's kind of cool.
So you have a valve to switch water to that Energy Filter off or on? Do you have two pumps too? One should be a little smaller and would be a "booster pump" for your Polaris. If you have that and it's off, that could also create your no pressure on that gauge. Well that and a valve that routes water to it or not.
Have you seen the inside of your cartridge filters? How do they look?
A Google search came up with this fitting that you could install.
USABlueBook - PVC Gauge Tee 1 NPTF, Pack of 4
I would try to install something like that somewhere in between your pump and cartridge filters. As far as a bleeder valve or "relief valve" you may be able to find something on Google as well. You ever do PVC work before?
So you have a valve to switch water to that Energy Filter off or on? Do you have two pumps too? One should be a little smaller and would be a "booster pump" for your Polaris. If you have that and it's off, that could also create your no pressure on that gauge. Well that and a valve that routes water to it or not.
Have you seen the inside of your cartridge filters? How do they look?
A Google search came up with this fitting that you could install.
USABlueBook - PVC Gauge Tee 1 NPTF, Pack of 4
I would try to install something like that somewhere in between your pump and cartridge filters. As far as a bleeder valve or "relief valve" you may be able to find something on Google as well. You ever do PVC work before?