I replaced the old single speed motor with a various speed motor. Now I noticed an issue. The way I set it up has been 3140RPM for 2 hrs, followed by 2100RPM for 4hrs, followed by 1300RPM for 6hrs. I think the setup can definitely make the whole pool of water circulate at least once per day. However, most cases are that when it runs at 3140RPM, the filter pressure is at about 30psi, and 15psi when it is @2100RPM and <5psi@1300RPM. When it is at 5psi, there is no water flow at all from the return line, and I can see instead of full of water, the pump basket are all air, which means the pump is running but without water being circulated at all during the last 6hrs of low speed RPM. (When I run @3140RPM, there are just several air bubbles in the pump basket, and @2100RPM, there are definitely a layer of air in it, but water still being circulated, not like @1300RPM. )
So my question is that, is this normal for various speed pumps? If it is not, what could be the issue? I actually haven't used the lowest 600RPM it provides. If I use that, then forget about it. there won't be any water pumped out at all. If it is normal, what is the rule of thumb of using various speed pump.
thank you very much.