Levels indicate the size of the particles the filters will remove.

Level 1 = 50 micron
Level 2 = 25 micron
Level 3 = 10 micron
Level 4 = 5 micron

Those filters will do NOTHING to change the water hardness. That is the job of the softener.

You say the filter in installed by the softener. Is it upstream or downstream from the softener? What size is the filter housing? It is entirely possible that it is too small for whole-house use.

So, level 4 would be better than level 1?

Yes, I am aware that the filter will do nothing to soften the water. I'm not sure which side of the softener it is on. Where should it be? I don't know what the size is, it's a standard housing on the waterline.

Since it's there, we are going to use it. Once we get moved in & live there a while (& save up from what we are spending to fix up the hour) we will be able to tweak & adjust as we need.

No, level 4 is not "better" than level 1. It will filter smaller particles at the expense of higher pressure drop. You use the lowest level that will remove the particulates in your water. Using a filter that is too fine will just impede water flow for no reason. Typically, 25 micron is a good place to start. 5 micron is really small, so avoid it unless it is absolutely necessary.

The filter should be upstream from your softener. If it is downstream, it is doing you no good -- don't bother placing a filter cartridge in it.

Thank you for your advice. I will start w/ the 25 micron & go from there. I don't think the water pressure is the best in that house.