When I refill water due to evaporation (5-10 gallons at a time). Do I need to refill using a hose through the filter area like when I do to fill the whole tub up?
In other words can I just pour buckets of water into the tub to add water due to evaporation loss. It's getting cold here in MN and I will bring my hoses in due to freezing.
The reason you fill through the filter when the spa is empty is so that you can get the water directly down into the pumps to displace the air inside them and help avoid the issue of air becoming entrapped in the pumps (especially the circ pump).
Therefore, if the spa is already mostly full and you're just "topping" it off there is no need to fill through the filter, just lay it inside the spa anywhere.